In this open, prospective, structured, naturalistic study of the efficacy of long-term treatment in social phobia 93 consecutive outpatients suffering from severe generalized or circumscribed social phobia (median Liebowitz Social Anxiety Scale score 83) and a high degree of concomitant psychiatric disease were administered treatment with moclobemide (712 +/- 75 mg/day at steady state). Fifty-nine patients who responded (Clinical Global Impression for Change: very much/much improved) completed 2 years of treatment. Patients then entered a drug-free period of at least 1 month during which 88% of the patients deteriorated. In a further 2-year treatment period with moclobemide those patients who had deteriorated became responders again. Symptoms recurred in a substantial number of the patients at the end of the study when the dose was reduced and then discontinued. Post-study follow up at 6-24 months after study completion found that 63.2% of patients were almost asymptomatic or had only mild symptoms, 15.8% were off all treatment, 28.1% were back on moclobemide, 10.6% were taking another psychotropic drug and 8.8% were in psychotherapy. All previous non-responders to moclobemide and mostly alcohol abusers (36.9%), had moderate or severe social phobia and were off all treatment (13.3%), on psychotherapy (15.9%) or on another psychotropic drug (8.8%). Discriminant analysis correctly predicted outcome in 93.5% of all patients. Alcohol abuse was by far the strongest predictor of negative outcome. Coexisting generalized anxiety disorder and dysthymia were less potent in this regard, whereas high baseline Hamilton anxiety or depression scale scores, circumscribed social phobia, or social phobia unassociated with avoidant personality disorder were predictors of a positive outcome. In conclusion, severe social phobia can be successfully treated in the long-term but many patients may need medication or psychotherapy for many years. Treatment should start as early as possible because complications such as alcohol abuse make treatment difficult.