Twenty-six young participants, 18-25 years, with social phobia (SP) were randomly assigned to eight 2-hour sessions of group mindfulness-based cognitive therapy (MBCT) and twelve 2-hour sessions of group cognitive-behavioral therapy (CBT) in a crossover design with participants receiving treatments in reversed order. Outcome was assessed after treatments, and at 6- and 12-month follow-ups. MBCT achieved moderate-high pre-post effect sizes (d=0.78 on a composite SP measure), not significantly different from, although numerical lower than those of CBT (d=1.15). Participants in both groups further improved in the periods following their first and second treatment until 6-months follow-up (pre-follow-up ds = 1.42 and 1.62). Thus, MBCT might be a useful, low cost treatment for SP, although, probably, less efficacious than CBT.