Previous neuropsychological studies demonstrated various deficits of impulse control in pathological gamblers (PGs). However, there are limited data available on response-inhibition impairment among PGs. The present study attempted to assess response inhibition in untreated PGs (N=83), in comparison with normal subjects (N=84). Go/no-go and target-detection conditions of a computerized task were used as a measure of response-inhibition ability. A repeated measures analysis of covariance (ANCOVA-RM) was used with response time, variability of response time, and number of false alarms and misses as dependent measures; group (PG and controls) as the between-subjects measure; condition (target detection or go/no-go) and time slice (first and second in each condition) as repeated measures within-subject factors; and educational level as a covariate. Our results showed that PGs were significantly more impaired in both target detection and go/no-go task performance than controls. The PGs had significantly more false alarms and misses than controls, and they were slower and less consistent in their responses.