Diamorphine was first legalized as a novel treatment option for heroin dependence in Germany in 2009. Today, specialized clinics in ten German cities provide diamorphine to heavily addicted patients. As the medical and societal context of diamorphine-assisted therapy is evolving, continued research into patients’ perceptions of opioid replacement therapy remains important. From February 2018 to June 2018, we conducted a survey study of outpatients on maintenance treatment with either diamorphine (n = 85) or methadone/levomethadone (n = 126). Patients were asked to complete a self-report questionnaire querying, besides socio-demographic information, the study participant’s satisfaction with the substitute drug, relapse with illicit drugs, patterns of craving, and alcohol consumption. Duration of opioid dependence did not differ significantly between groups. Patients on diamorphine were approximately 3 years younger than patients on methadone/levomethadone. They also had a higher frequency of daily intake of their substitute drug and had had their dosage adjusted more often during the preceding 6 months. Still, diamorphine patients reported greater satisfaction with their substitute drug in tandem with significant reductions in relapse-related behaviors and cravings. While the most common relapse reported by patients on methadone replacement was heroin relapse (68%), most instances of illicit drug use in the diamorphine group involved cocaine (48%). Although self-reported alcohol consumption did not differ significantly between groups, a higher percentage of diamorphine patients than methadone patients endorsed decreased alcohol consumption since entering therapy. Taken together, these findings point to meaningful differences between diamorphine and methadone/levomethadone in opioid replacement therapy