To assess the long-term safety and tolerability of tegaserod in patients with chronic constipation (CC). This 13-month, uncontrolled extension study enrolled CC patients who completed a 12-wk randomized, double-blind, placebo-controlled core study. Patients receiving tegaserod 6 or 2 mg b.i.d. during the core study continued on the same dose; those receiving placebo were switched to tegaserod 6 mg b.i.d (placebo-to-tegaserod). Safety and tolerability were assessed by monitoring adverse events (AEs), laboratory parameters, vital signs, and electrocardiograms. Symptom evaluations included patient satisfaction with bowel habit and bothersomeness of constipation, abdominal distension/bloating, and abdominal discomfort/pain. A total of 842 patients entered the extension study; 451 (54%) completed. AEs typically occurred within the first month of tegaserod treatment. Long-term treatment neither increased AE incidence nor revealed new safety risks. Headache (11.3%, 14.5%, and 16.1% in the tegaserod 6 mg b.i.d., 2 mg b.i.d., and placebo-to-tegaserod groups, respectively) and abdominal pain (8.8%, 8.8%, 10.9%) were the most common AEs. Diarrhea, the most common drug-related AE (4.9%, 2.5%, 8.0%), rarely led to discontinuation (0.7%, 0.0%, 2.2%). Diarrhea was transient, resolved without treatment interruption or rescue medication, and had no clinically significant consequences. Of 27 serious AEs, none were considered treatment related. No deaths or reports of ischemic colitis occurred in tegaserod-treated patients. No clinically relevant changes occurred in other safety parameters. Safety findings were similar in patients switched from placebo to tegaserod and those maintained on tegaserod. Tegaserod has a favorable safety profile and is well tolerated during continuous long-term treatment in patients with CC.