Background: People with serious mental illness (SMI) experience numerous barriers to developing and maintaining friendships. Aims: To explore the benefits and drawbacks of an intentional friendship programme (Compeer, Inc), which develops new social relationships for people with SMI by matching them in one-to-one relationships with community volunteers for weekly social activities. Methods: Twenty clients and volunteers, in Compeer friendships for different lengths of time, participated in individual semi-structured qualitative inter-views. Several volunteers were themselves current or former consumers of mental health services. Results: Participants reported numerous benefits to participating in Compeer. Clients and volunteers spoke enthusiastically about the benefits of gaining a friend. Many intentional relationships deepened over several years into mutually beneficial friendships. Most clients became more outgoing, sociable and active, with increased self-esteem, self-worth and self-confidence. Volunteers who had experienced mental illness themselves provided unique added benefits to the relationship. Drawbacks were minimal and financial and other costs to volunteers were low. Conclusions: Intentional friendships can be a potent yet cost-effective way to help people with SMI develop social skills, expand their social networks, and im-prove their quality of life. However, because relationships take several years to develop, quantitative evaluations using short follow-up periods may underestimate programme effectiveness. Key words: serious mental illness, intentional friendship, befriending, social support, community integration