OBJECTIVE: Several classes of medications have demonstrated efficacy in panic disorder, but direct comparison of 2 proven treatments is still uncommon. The purpose of this study was to compare sertraline and paroxetine in the acute treatment of panic disorder. METHOD: Adult outpatients with panic disorder with or without agoraphobia (DSM-IV and ICD-10 criteria) were randomly assigned in double-blind fashion to 12 weeks of treatment with flexible doses of sertraline (titrated up to 50-150 mg/day; N = 112) or paroxetine (titrated up to 40-60 mg/day; N = 113). Patients were then tapered off medication over 3 weeks. The primary analysis was a noninferiority analysis of Panic and Agoraphobia Scale (PAS) scores. Secondary measures included panic attack frequency and the Clinical Global Impressions-Improvement scale (CGI-I) (with responders defined as those with a CGI-I score < or = 2). Data were collected from January 2000 to June 2001. RESULTS: Sertraline and paroxetine were associated with equivalent levels of improvement on the PAS total score, as well as on all secondary outcome measures. Eighty-two percent of patients taking sertraline versus 78% of those taking paroxetine were CGI-I responders at endpoint. Numerically more patients on paroxetine treatment compared with sertraline treatment discontinued due to adverse events (18% vs. 12%; NS), and a significantly higher proportion of paroxetine patients showed > or = 7% weight gain (7% vs. < 1%; p <.05). During the taper period, the proportion of panic-free patients increased by 4% with sertraline but decreased by 11% with paroxetine (p <.05). CONCLUSION: Sertraline and paroxetine had equivalent efficacy in panic disorder, but sertraline was significantly better tolerated and was associated with significantly less clinical worsening during taper than paroxetine.