Impaired control leading to excessive gambling and subsequent adverse consequences is the primary feature of pathological gambling. Defined as an impulse control disorder, elevated traits of impulsivity are associated with increased levels of intensity of gambling and symptoms severity and are predictive of treatment dropout. However, to date, research has failed to explore the differential effects of functional and dysfunctional impulsivity in gambling and the relationship between these two forms of impulsivity to treatment compliance and treatment outcome. This study investigates the interrelationship between functional and dysfunctional impulsivity as measured by the scale, gambling severity, substance use and depression in a clinical sample of 60 pathological gamblers seeking cognitive-behavioural therapy. Results indicate that dysfunctional impulsivity is associated with poorer response to treatment but not with treatment completion.