This review was designed to provide a detailed analysis of long-term outcome data from treatment studies for panic disorder, with the goal of ascertaining differential efficacy of the available treatments. Studies were included if they were published after 1980 and if follow-up took place at least 6 months after treatment termination. Thirty-one studies were located. A variety of methodological problems were found in these studies, including lack of clarity of diagnosis, lack of clarity in the treatment administered, and inadequately tracked nonstudy treatments during the study and follow-up periods, which limited the information that could be obtained about long-term outcome. Long-term outcome studies that closely track the additional treatments that patients receive are necessary to draw more definitive conclusions about differential treatment efficacy for panic disorder. Available data suggest that there is limited evidence for long-term maintenance of short-term treatment gains in panic disorder patients in the absence of continued treatment.