People with rheumatoid arthritis (RA), often associated with psychosocial problems and reduced quality of life, benefit from the guidance of trained medical social workers. This study explores the effectiveness of psychosocial treatment in patients with RA using a structured interview to detect psychosocial problems for 100 patients. These individuals were offered regular sessions with a medical social worker. Three types of mixed-problems were found: mixed problems related to RA, mixed problems related to the life situation, and mixed problems related to a combination of RA and the life situation. The RA patients who reported mixed-problems at time of their diagnosis received psychosocial treatment from a medical social worker regardless of the mixed problems they experienced. In addition, we found that disease-related mixed problems seemed more treatable than other problems. Social work in somatic healthcare seems most successful in patients with sickness-related social and psychosocial problems.