The selegiline transdermal system (STS) is a monoamine oxidase inhibitor (MAOI) with unique pharmacokinetic and pharmacodynamic properties that was developed to overcome limitations of orally administered MAOIs, particularly dietary tyramine restrictions. We present data from a long-term study assessing the safety and efficacy of initial and continuation STS therapy in patients with major depressive disorder (MDD). After 10 weeks of treatment with STS 6 mg/24 h, 322 patients who responded with a 17-item Hamilton Depression Rating Scale score of 10 or less were randomly assigned to double-blind treatment with STS 6 mg/24 h or placebo for 52 weeks. Relapse was defined as meeting the following criteria on 2 consecutive visits: (1) 17-item Hamilton Depression Rating Scale score of 14 or more, (2) a Clinical Global Impression of Severity score of 3 or more with a 2-point increase from double-blind baseline, and (3) the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria for a major depressive episode. At study week 52, significantly fewer STS patients experienced relapse of major depressive episode (25/149 [16.8%]) compared with placebo (50/163 [30.7%]) (P = 0.0025). In addition, patients receiving STS experienced a significantly longer time to relapse compared with those receiving placebo (P = 0.0048). The safety profile of STS was similar to placebo, with the exception of application-site reactions (STS, 15.2%; placebo, 3.7%). No cases of hypertensive crisis were reported, despite the lack of requirement for dietary tyramine restrictions. In conclusion, STS was well tolerated and efficacious in maintaining a sustained response in MDD patients. The results of this study suggest that STS may be suitable in the long-term treatment of MDD.