Diabetic patients are traditionally taught to discard plastic syringe/needle units after a single use and to employ aseptic technique for administering insulin injections. We surveyed 87 diabetic outpatients for compliance with aseptic recommendations. We then studied prospectively the effects of reusing disposable syringes in 56 diabetic patients who reused syringes a mean of 6.6 times for 8.3 months and an aggregate of 23,664 injections. Almost half (49%) of diabetic patients in a combined university clinic and private practice reused supposedly disposable insulin syringes a mean of 3.9 times. Compliance with standard aseptic precautions was poor, with only 29% of patients following recommended practices. No adverse effect of syringe reuse was identified. The authors conclude that diabetic patients frequently reuse disposable syringes, without apparent harmful effect.