The main purpose of the present study is to investigate the differences between alcoholics and heroin addicts in some relapse dimensions and self-efficacy. The sample consisted of 180 inpatient males, who admitted to Al-Amal Hospital, Jeddah, Saudi Arabia, for treatment from substance abuse. The total sample was divided into two groups: 105 participants were heroin addicts and 75 were alcoholics. Two standardized questionnaires [inventory of drug taking situations (IDTS) and situational confidence questionnaire (SCQ)] were used. Heroin addicts have statistically significant high mean IDTS scores compared with the alcoholics sample, whereas the alcoholics have significantly higher mean SCQ scores than did their heroin counterpart. Again, the alcoholics had significantly lower admission and relapse rates compared with the heroin group. Furthermore, the results indicate that the highest high-risk relapse situations are negative emotions (NE), testing personal control (TPC), social pressure (SP), and urge and temptations (UT).