IMPORTANCE The ultra high-risk (UHR) criteria were introduced to prospectively identify patients at high risk of psychotic disorder. Although the short-term outcome of UHR patients has been well researched, the long-term outcome is not known. OBJECTIVE To assess the rate and baseline predictors of transition to psychotic disorder in UHR patients up to 15 years after study entry. DESIGN Follow-up study of a cohort of UHR patients recruited to participate in research studies between 1993 and 2006. SETTING The Personal Assessment and Crisis Evaluation (PACE) clinic, a specialized service for UHR patients in Melbourne, Australia. PARTICIPANTS Four hundred sixteen UHR patients previously seen at the PACE clinic. MAIN OUTCOMES AND MEASURES Transition to psychotic disorder, as measured using the Comprehensive Assessment of At-Risk Mental States, Brief Psychiatric Rating Scale/Comprehensive Assessment of Symptoms and History, or state public mental health records. RESULTS During the time to follow-up (2.4-14.9 years after presentation), 114 of the 416 participants were known to have developed a psychotic disorder. The highest risk for transition was within the first 2 years of entry into the service, but individuals continued to be at risk up to 10 years after initial referral. The overall rate of transition was estimated to be 34.9%over a 10-year period (95%CI, 28.7%-40.6%). Factors associated with transition included year of entry into the clinic, duration of symptoms before clinic entry, baseline functioning, negative symptoms, and disorders of thought content. CONCLUSIONS AND RELEVANCE The UHR patients are at long-term risk for psychotic disorder, with the highest risk in the first 2 years. Services should aim to follow up patients for at least this period, with the possibility to return for care after this time. Individuals with a long duration of symptoms and poor functioning at the time of referral may need closer monitoring. Interventions to improve functioning and detect help-seeking UHR patients earlier also may be indicated.