Pathological and problem gambling refer to a class of disorders, including those meeting criteria for a psychiatric diagnosis (i.e., pathological gambling), and others comprising a spectrum of severity defined by significant personal and social harm (i.e., problem gambling), that may be common in substance use treatment but are frequently unrecognized. This paper presents a systematic review and meta-analysis of available evidence indicating the prevalence of such gambling disorders in substance use treatment. It provides weighted mean estimates from across studies of clinical samples of substance users, and suggests around 14 of patients that demonstrate comorbid pathological gambling. Around 23 suffer conditions along the broader spectrum of problem gambling. The review also highlights important limitations of existing evidence, including scant data on current versus lifetime comorbidity, as well as reliance on convenience samples and self-administered measures of gambling problems. Notwithstanding a concomitant need for caution when applying these results, the findings suggest a strong need to identify and manage gambling comorbidity in substance use treatment. Strategies for identification of gambling disorders, and therapies that may provide useful adjunctive interventions in substance use treatment are discussed.