The paper investigates whether the changes in cognitive appraisal and coping strategies related to initiation of insulin treatment onset mediate the effect of temperament on changes in positivity ratio among diabetic patients. Temperament, cognitive appraisal, coping strategies and positivity ratio were assessed among 278 patients: just before conversion to insulin therapy and then one month later. Mediation analysis indicated that endurance and briskness were directly connected to changes in positivity ratio, whilst the effect of perseveration on positivity ratio was indirect (...) via changes in negative appraisal, emotion- and problem-focused coping. The results confirm the stressful nature of the initiation of insulin treatment, and the assumptions of Lazarus’ model of stress and regulative role of temperament. (shrink)