AIMS: To compare quality of life (QoL) and treatment satisfaction in patients with Type 1 diabetes receiving the rapid-acting insulin analogue, insulin aspart (IAsp), with that in patients receiving soluble human insulin (HI). METHODS: In this 6-month, multinational, randomized, open-label trial, 424 patients from German-speaking countries were subjected to psychometric assessment before and after randomization (ratio 2 : 1) to basal-bolus treatment with either IAsp (n = 283) or HI (n = 141). Patients on HI were advised to keep an injection-meal interval of 30 min, whereas patients on IAsp were advised to inject immediately before meals. Treatment satisfaction and diabetes-related QoL were assessed using validated instruments to measure the domains of patients' individual treatment goals, physical complaints, worries about the future, social relations, leisure time flexibility, daily hassles, diet restrictions, burdens and fear of hypoglycaemia, blood glucose fluctuations, self-efficacy, and fear of insulin analogues. RESULTS: After 6 months, IAsp was associated with significantly greater improvement in treatment satisfaction than HI in two different scales (P < 0.01), and in QoL with respect to diet restrictions (P < 0.01). Improved satisfaction was mainly due to increased dietary and leisure time flexibility (P < 0.0001). Twenty-three percent of the IAsp group vs. 14% of the HI group achieved small but important improvements of total QoL (between-group difference, P < 0.06). The number needed to treat (NNT) with IAsp for an important increase in QoL was calculated to be 10. Regression analyses of potential predictors of improvement in QoL highlighted patients intensely striving for physical strength (P < 0.01; NNT = 7) and patients feeling less protected against hypoglycaemia (P < 0.005; NNT = 8) as being the most likely to benefit from IAsp. CONCLUSIONS: Under these study conditions, IAsp improved treatment satisfaction and quality of life regarding diet restrictions when compared with human insulin. The 'numbers needed to treat' for important quality of life benefits indicate that the effect of IAsp in this regard is not trivial.