The interference of background characteristics with quality of life and metabolic control in patients with insulin-dependent diabetes mellitus (IDDM) were examined. Seventy-three consecutive outpatients who switched from syringe injections to multiple pen-injection treatment comprised the study group. Perceived status as well as retrospective changes in quality of life, attributed to the new treatment modality, were assessed at follow-up after 9-13 months. Data on metabolic control (HbA1C) were collected at base-line and follow-up. Sub-group comparisons in life quality and metabolic control were performed with regard to differences in sex, age, cohabitation, onset and duration of IDDM. Most of the background characteristics had no or just minor significance for status and change in the life quality and metabolic control of the patients. Cohabitation, however, was linked to a better life quality status pertaining to different domains and a tendency to better metabolic control. In addition, females reported a slightly better health status and a more healthy life style (i.e. eating, drinking and smoking habits) than did males. Extra treatment attention may therefore be justified for non-cohabiting males.