A 77-year-old man with type II diabetes taking a stable dose of subcutaneous, twice daily human insulin developed symmetrical, inflammatory, rheumatoid factor positive polyarthritis. Within 2 weeks of starting therapy with prednisone 5 mg daily and hydroxychloroquine 400 mg daily he had 2 episodes of severe hypoglycemic coma requiring emergency care. His blood glucose became controlled again when his insulin was decreased by 37%. There are no reported cases of hypoglycemia in diabetic or nondiabetic patients treated with hydroxychloroquine. Hydroxychloroquine has been reported to reduce insulin requirements in refractory type II diabetes by an average of 30%. When hydroxychloroquine is initiated for the treatment of polyarthritis in a type II diabetic requiring insulin or sulfonylurea treatment, blood glucose levels should be monitored closely and the insulin dose may need to be reduced.