Background : Evidence for the effectiveness of treatments for subjects at ultrahigh risk (UHR) for developing psychosis remains inconclusive. Objective : A new cognitive behavioral intervention specifically targeted at cognitive biases (ie, Cognitive Behavioral Therapy [CBT] for UHR patients plus treatment as usual [TAU] called CBTuhr) is compared with TAU in a group of young help-seeking UHR subjects. Methods : A total of 201 patients were recruited at 4 sites and randomized. In most cases, CBTuhr was an add-on therapy because most people were seeking help for a comorbid disorder. The CBT was provided for 6 months, and the follow-up period was 18 months. Results : In the CBTuhr condition, 10 patients transitioned to psychosis compared with 22 in the TAU condition (χ ( 2 ) (1) = 5.575, P = .03). The number needed to treat (NNT) was 9 (95% confidence interval [CI]: 4.7-89.9). At 18-month follow-up the CBTuhr group was significantly more often remitted from an at-risk mental state, with a NNT of 7 (95% CI: 3.7-71.2). Intention-to-treat analysis, including 5 violations against exclusion criteria, showed a statistical tendency (χ ( 2 ) (1) = 3.338, P = .06). Conclusions : Compared with TAU, this new CBT (focusing on normalization and awareness of cognitive biases) showed a favorable effect on the transition to psychosis and reduction of subclinical psychotic symptoms in subjects at UHR to develop psychosis.