AB In the current paper, the prevalence of pathological gambling in 112 treatment-seeking patients with substance addiction (81 alcoholics and 31 cocaine dependents) was estimated. The DSM-IV-TR diagnostic criteria for pathological gambling and the Spanish version of the South Oaks Gambling Screen (SOGS) were used. The results showed that 22.3% of substance-addicted patients had a comorbid diagnosis of pathological gambling. Furthermore, an additional 11.6% of the sample had relevant symptoms for problem gambling. In sum, 33.9% of the sample reported clinically significant gambling-related symptoms. From a socio-demographic point of view, all substance-addicted patients with gambling-related symptoms were men. A comparison between substance-addicted patients with and without pathological gambling showed significant differences in alcohol severity (assessed by the EuropASI), psychopathological symptoms (assessed by the SCL-90-R) and personality variables (assessed by the MCMI-II). In all cases, scores were significantly higher in gamblers than in non-gamblers. Finally, the implications of these results for further research and clinical practice are commented upon.