diff --git a/crates/typedialog-core/src/form_parser/conditions.rs b/crates/typedialog-core/src/form_parser/conditions.rs
index fd0421a..45faf97 100644
--- a/crates/typedialog-core/src/form_parser/conditions.rs
+++ b/crates/typedialog-core/src/form_parser/conditions.rs
@@ -3,6 +3,7 @@
 //! Provides logic for evaluating `when` conditions on form elements.
 
 use std::collections::HashMap;
+use std::path::Path;
 
 use super::types::FormDefinition;
 
@@ -120,9 +121,16 @@ pub fn should_load_fragment(
 /// - "field_name contains value"
 /// - "field_name startswith value"
 /// - "value in field_name" (array membership)
+/// - "file_exists(path)" (file existence check)
+/// - "!file_exists(path)" (negated file existence check)
 pub fn evaluate_condition(condition: &str, results: &HashMap<String, serde_json::Value>) -> bool {
     let condition = condition.trim();
 
+    // Check for function calls first (file_exists, etc.)
+    if let Some(result) = evaluate_function_call(condition) {
+        return result;
+    }
+
     // Check string operators first (word boundaries)
     let string_operators = ["contains", "startswith", "endswith", "in"];
     for op_str in &string_operators {
@@ -246,6 +254,44 @@ pub fn evaluate_condition(condition: &str, results: &HashMap<String, serde_json:
     true
 }
 
+/// Evaluate function calls in conditions
+/// Returns Some(bool) if a function call was found and evaluated
+/// Returns None if no function call was found
+fn evaluate_function_call(condition: &str) -> Option<bool> {
+    let condition = condition.trim();
+
+    // Handle negation prefix
+    let (is_negated, clean_condition) = if let Some(stripped) = condition.strip_prefix('!') {
+        (true, stripped.trim())
+    } else {
+        (false, condition)
+    };
+
+    // Check for file_exists() function
+    if clean_condition.starts_with("file_exists(") && clean_condition.ends_with(')') {
+        let start = "file_exists(".len();
+        let end = clean_condition.len() - 1;
+        let path_arg = clean_condition[start..end].trim();
+
+        // Remove quotes if present
+        let path = if (path_arg.starts_with('"') && path_arg.ends_with('"'))
+            || (path_arg.starts_with('\'') && path_arg.ends_with('\''))
+        {
+            &path_arg[1..path_arg.len() - 1]
+        } else {
+            path_arg
+        };
+
+        // Check if file exists
+        let exists = Path::new(path).exists();
+
+        // Apply negation if needed
+        return Some(if is_negated { !exists } else { exists });
+    }
+
+    None
+}
+
 /// Parse a value from condition right-hand side
 fn parse_condition_value(s: &str) -> serde_json::Value {
     let s = s.trim();
@@ -467,4 +513,87 @@ mod tests {
         assert!(evaluate_condition("enable_feature == true", &results));
         assert!(evaluate_condition("name == test", &results));
     }
+
+    #[test]
+    fn test_file_exists_with_existing_file() {
+        let results = HashMap::new();
+
+        // Create a temporary file
+        let temp_dir = std::env::temp_dir();
+        let test_file = temp_dir.join("typedialog_test_file.txt");
+        std::fs::write(&test_file, "test content").unwrap();
+
+        // Test with double quotes
+        let condition = format!("file_exists(\"{}\")", test_file.display());
+        assert!(evaluate_condition(&condition, &results));
+
+        // Test with single quotes
+        let condition = format!("file_exists('{}')", test_file.display());
+        assert!(evaluate_condition(&condition, &results));
+
+        // Test without quotes
+        let condition = format!("file_exists({})", test_file.display());
+        assert!(evaluate_condition(&condition, &results));
+
+        // Clean up
+        std::fs::remove_file(&test_file).unwrap();
+    }
+
+    #[test]
+    fn test_file_exists_with_nonexistent_file() {
+        let results = HashMap::new();
+
+        // Use a path that definitely doesn't exist
+        let nonexistent = "/tmp/typedialog_nonexistent_file_12345.txt";
+
+        let condition = format!("file_exists(\"{}\")", nonexistent);
+        assert!(!evaluate_condition(&condition, &results));
+    }
+
+    #[test]
+    fn test_file_exists_negated() {
+        let results = HashMap::new();
+
+        // Create a temporary file
+        let temp_dir = std::env::temp_dir();
+        let test_file = temp_dir.join("typedialog_test_negation.txt");
+        std::fs::write(&test_file, "test").unwrap();
+
+        // Negated: should return false for existing file
+        let condition = format!("!file_exists(\"{}\")", test_file.display());
+        assert!(!evaluate_condition(&condition, &results));
+
+        // Clean up
+        std::fs::remove_file(&test_file).unwrap();
+
+        // After removal, negated should return true
+        let condition = format!("!file_exists(\"{}\")", test_file.display());
+        assert!(evaluate_condition(&condition, &results));
+    }
+
+    #[test]
+    fn test_file_exists_with_directory() {
+        let results = HashMap::new();
+
+        // Test with an existing directory
+        let temp_dir = std::env::temp_dir();
+        let condition = format!("file_exists(\"{}\")", temp_dir.display());
+
+        // Path::exists() returns true for both files and directories
+        assert!(evaluate_condition(&condition, &results));
+    }
+
+    #[test]
+    fn test_file_exists_with_relative_path() {
+        let results = HashMap::new();
+
+        // Create a file in current directory
+        std::fs::write("typedialog_test_relative.txt", "test").unwrap();
+
+        let condition = "file_exists(\"typedialog_test_relative.txt\")";
+        assert!(evaluate_condition(condition, &results));
+
+        // Clean up
+        std::fs::remove_file("typedialog_test_relative.txt").unwrap();
+    }
 }