The effect of flecainide on painful diabetic neuropathy was studied in 10 patients suffering from pain for one or more months of duration and severe enough to disturb daily life. Among them, 8 patients had been inadequately treated with conventional agents such as carbamazepine, tiapride and mexiletine. In 5 of them, painful symoptoms were due to posttreatment diabetic neuropathy. Three patients had diabetic retinopathy, but none had signs of diabetic nephropathy. Flecainide (50 mg p.o., b. i. d. or t. i. d.) was given over a period of 4 weeks after 2 weeks of baseline observation. The effects were assessed in terms of pain score based on subjective reports. Within 2 weeks, the pain score was significantly reduced to 6.8/10 and within 4 weeks to 4.1/10. However, neurological findings remained unchanged. No side effects, including ECG changes, were noted in these 10 patients during the study. These results suggest that flecainide is useful for the treatment of painful diabetic neuropathy.