OBJECTIVES: A recent study showed that 4mm pen needle (PN) has significantly lowered risk of intramuscular insulin injection and thus reduced risk of hypoglycemia. It is important, however, to understand whether diabetes patients are well adapted to 4mm PN when switched from longer needles. The study is to evaluate the difference in patient perception and outcomes before and after switching to the new 4mm PN. METHODS: A prospective pilot survey study was conducted from August 2011 to March 2012 in two public hospitals in Hong Kong. Thirty-four subjects with diabetes on longer PN (8mm, 6mm or 5mm) were randomly selected and consented to switch to 4mm PN for two to four weeks. Questionnaires included perception and outcomes Five-point Likert scales were employed to measure pain level, satisfaction level, insulin leakage, injection pressure, and ease of injection to different body areas pre- and post- switch of longer to shorter PN.  Insulin leakage volume pre- and post switch was compared using a droplet size chart representing 1uL, 10uL, 20uL, and 40uL. Statistical analyses were conducted using SAS (v9.1). RESULTS: The overall response rate was 94.1% (N=32). Demographics of respondents: 48.9±18.6 years (13-76 years); 64.5% females; 46.7% T1DM; A1C: 8.7±1.7% (5.7-12.7%); BMI: 24.0±45.1kg/ m2 (17.5-40.0kg/m2); average insulin dosage: 46.9±18.6U (6-86U). Of all analyzed, 33.3% generally injected with high speed to avoid pain.  There was no significant difference in the volume of insulin leakage pre- and post PN switch when injecting on abdomen (p= 0.7530) or thigh (p=0.5637); no significant difference in level of pain (p=0.0519). CONCLUSIONS: The use of 4mm PN showed no difference in outcomes and perception of use when switched from 8, 6, 5 mm PN in a heterogeneous sample with obese, overweight, normal and skinny patients. A tendency of preference towards 4mm PN with lower pain level and less leakage may be observed with larger sample size.