AIMS: Reusing insulin pen needles could help to reduce the increasing economic burden of diabetes. We tested the hypothesis that reusing insulin pen needles leads to needle tip deformity and increased pain. METHODS: Three blinded reviewers assessed 123 electron microscope pictures analyzing needle tip deformity of insulin pen needles used up to four times by diabetic subjects and up to five times by blinded non-diabetic volunteers. The estimated frequency of needle use was correlated to the actual number of needle use. Pain intensity and unpleasantness of each injection were measured by a visual analogue scale and their differences analyzed by Kruskal-Wallis analysis of variance. RESULTS: Unused needles could be differentiated visually from used needles. However, there was no correlation between the actual and guessed number of times a needle was used (r = 0.07, P = 0.2). Evaluating all 270 injections, neither pain intensity nor unpleasantness increased with repeated injections of the same needles in people with diabetes (P = 0.1 and 0.96) and in the volunteers (P = 0.63 and 0.92). CONCLUSIONS: Using pen needles four to five times does not lead to progressive needle tip deformity and does not increase pain intensity or unpleasantness, but could increase convenience and lead to substantial financial savings in Europe of around EUR 100 million/year.