BACKGROUND Addictive disorders are an epiphenomenon of underlying vulnerabilities. Research over the past decades into these vulnerabilities has distinguished internalizing and externalizing spectra as two distinct personality factors underlying substance use disorders (SUDs). In this study, we explore the behavioral activation and inhibition factors in patients with SUD. METHODS A total of 240 patients with SUD were recruited for the study. Behavioral inhibition system-behavioral activation/approach system (BIS-BAS) scale was used to assess the three domains of the behavioral activation, namely drive, fun seeking and reward responsiveness, and the behavioral inhibition as a single domain. BIS and BAS subscale total scores, inter-domain correlation, factor structure, and difference in the early-onset and late-onset SUD subgroup scores were calculated. RESULTS The drive, fun seeking, and reward responsiveness showed a moderate degree of correlation among each other ranging from 0.30 to 0.36. The behavioral inhibition subscale had a modest correlation r = 0.26 with the reward responsiveness subdomain of behavioral activation. The factor structure remained valid at two- and four-factor solutions apart from few items with inconsistent loading. The early-onset n = 209 (87.1%) and late-onset n = 31 (12.9%) SUD subgroup analysis showed a statistically significant difference in the mean scores of drive and fun-seeking subscales with P < 0.05. CONCLUSIONS Behavioral activation and inhibition remain two valid personality factors in patients with SUDs. Patients with early onset of SUD have a significantly higher behavioral activation scores in the drive, and fun-seeking subfactors suggesting a higher externalizing tendency.