PURPOSE: The aims of this study were to assess the results of biofeedback treatment in constipated patients and to identify variables that might be used to predict the outcome. METHOD: Twenty-eight patients (5 men; median age, 46 (range, 22-72) years) with any degree of paradoxical activation measured with thin hook needle electromyography in the external sphincter or puborectalis muscle were included. The symptom duration varied between I and 30 (median, 9) years. The patients had eight outpatient training sessions with electromyography-based audiovisual feedback. All patients were followed up prospectively with a validated bowel function questionnaire from which a symptom index was created. RESULTS: At three months, nine patients had no improvement and underwent other treatments. The remaining 19 patients were followed up for a median of 14 (range, 12-34) months. Twelve patients (43 percent) stated they had improved rectal emptying. A good result was associated with increased stool frequency (P < 0.05), improved symptom index (P < 0.01), and reduction of laxative use (P < 0.05). A long symptom duration, a high pretreatment symptom index, and laxative use were related to a poor result (P < 0.01-0.05). The improved group had less perineal descent (P < 0.05), and a prominent puborectalis impression on defecography tended to be more common (P = 0.06). CONCLUSION: With the use of wide inclusion criteria, biofeedback was successful in 43 percent of patients, with a treatment effect lasting at least one year. The results suggest that biofeedback should be used as the initial treatment of constipated patients with a paradoxical puborectalis contraction.