BACKGROUND The prognostic value of a J wave and ST-segment morphology after J wave in inferolateral leads in Brugada syndrome (BS) is still unknown. OBJECTIVE To evaluate the prognostic value of a J wave and ST-segment morphology after J wave in a large Japanese cohort of BS. METHODS A total of 460 consecutive patients with BS (mean age 52±14 years, 432 men) were enrolled. The presence and location of leads showing a J wave, ST-segment morphology after J wave, and clinical outcomes were evaluated in patients with documented ventricular fibrillation (VF) (N = 84), those with syncope without documented VF (N = 109), and subjects without symptoms (N = 267). RESULTS The prevalence of a J wave in the inferior and/or lateral leads was 12% (53 cases). The prevalence of a J wave among the 3 groups was not different. The incidence of cardiac events (sudden cardiac death or VF) during a mean follow-up period of 50±32 months was not different in patients with (11%) or without (8%) a J wave. Patients with a J wave in both inferior and lateral leads or with horizontal ST-segment morphology after J wave showed a higher incidence of cardiac events than those without (P = .04 and .02, respectively). Multivariate analysis revealed symptoms, QRS duration in lead V2>90 ms, and inferolateral J wave and/or horizontal ST-segment morphology after J wave were important for predicting cardiac events. CONCLUSIONS The presence of a J wave in multiple leads and horizontal ST-segment morphology after J wave may indicate a highly arrhythmogenic substrate in patients with BS.