This pilot study evaluated the experience of people with co-occurring disorders (mental illness and addiction) in relation to peer-led and professional-led group interventions. The study used a qualitative (phenomenological) approach to evaluate the experience of a convenience sample of 6 individuals with co-occurring disorders who participated in up to 8 sessions each of both peer-led and professional-led group interventions (with a similar rate of attendance in both groups). The semi-structured interview data were coded and thematically analyzed. We found 5 themes within and across the 2 interventions. In both groups, participants experienced a positive environment and personal growth, and learned, albeit different things. They were more comfortable in the peer-led group and acquired more knowledge and skills in the professional-led group. Offering both peer-led and professional-led group interventions to people with co-occurring disorders may be better than offering either alone.