Prognostic groups defined by lactate dehydrogenase concentration and number of organ sites containing metastases have been reported for patients treated with dabrafenib and trametinib for advanced melanoma. We aimed to validate these prognostic groups for patients treated with vemurafenib and cobimetinib in the coBRIM and BRIM-3 clinical studies. Eight hundred nine patients were included, 240 treated with vemurafenib plus cobimetinib and 569 with vemurafenib. For patients treated with vemurafenib and cobimetinib, both overall survival (P < 0.001, c-statistic = 0.72) and progression-free survival (P < 0.001, c-statistic = 0.65) differed markedly between prognostic groups. Two-year progression-free survival ranged from 3 (lactate dehydrogenase ≥2 times the upper limit of normal) to 50% (normal lactate dehydrogenase and ≤3 sites), and two-year overall survival ranged from 7 to 71%. For patients treated with vemurafenib monotherapy, overall survival (P < 0.001, c-statistic = 0.66) and progression-free survival (P < 0.001, c-statistic = 0.62) also differed significantly between prognostic groups. In conclusion, prognostic groups identified for patients treated with dabrafenib and trametinib are also applicable to patients treated with vemurafenib and cobimentinib.