Regional anesthesia in the obese patient can be challenging and possibly carries a greater failure rate as compared with that in the non-obese patient. We retrospectively reviewed our prospectively gathered peripheral block data to determine the influence of body weight on success rate of the supraclavicular block. Obesity was defined as body mass index > or =30. The overall success rate was 97.3% in nonobese and 94.3% in obese patients (P < 0.01). Residents completed 80% of the blocks in nonobese patients and 73% in obese patients (P < 0.01). No difference in acute complications was observed. Obesity is associated with a slight decrease in success rate of supraclavicular block and an increase in its relative difficulty without apparent effect on acute complications.