The aim of the study was to evaluate safety, efficacy and acceptability of a pre-filled insulin pen device (NovoLet) in diabetic patients over 60 years old already treated with insulin administered with conventional syringes. After a run-in period of 2 weeks, 60 patients participated in a randomized cross-over study with two 6-week treatment periods using the insulin pen or conventional syringes. Insulin regimens did not change during the study. Hypoglycaemic episodes did not differ significantly between both kinds of treatment and no severe hypoglycaemia was registered. HbAlc (%) was (mean +/- S.D.) 7.7 +/- 1.2 and 7.9 +/- 1.1 during pen and syringe treatment, respectively. Blood glucose profiles were similar during both treatment modalities except for pre-lunch blood glucose values (mmol/l) lower during pen treatment (8.7 +/- 2.9 vs. 9.2 +/- 2.7, P < 0.01). The insulin dose (U/day) was 31.9 +/- 8.9 (pen) and 32.3 +/- 9 (syringe). 54 patients found the functioning of the insulin pen easy to understand and preferred it for future treatment because the conditions of insulin administration are faster and easier than with conventional syringes. We concluded that the pre-filled insulin pen is safe, efficacious and is highly accepted in over 60 years old diabetic patients.