OBJECTIVE: Carbohydrate counting is an effective approach to mealtime insulin adjustment in type 1 diabetes but has not been rigorously assessed in type 2 diabetes. We sought to compare an insulin-to-carbohydrate ratio with a simple algorithm for adjusting the dose of prandial insulin glusiline. RESEARCH AND DESIGN METHODS: This 24-week, multicenter, randomized, controlled study compared two algorithms for adjusting mealtime (glulisine) insulin along with a standard algorithm for adjusting background (glargine) insulin in 273 intent-to-treat patients with type 2 diabetes. Glulisine and glargine were adjusted weekly in both groups based on self-monitored blood glucose (SMBG) results from the previous week. The simple algorithm group was provided set doses of glulisine to take before each meal. The carbohydrate counting (carb count) group was provided an insulin-to-carbohydrate ratio to use for each meal and adjusted their glulisine dose based on the amount of carbohydrate consumed. RESULTS: A1C levels at week 24 were 6.70% (simple algorithm) and 6.54% (carb count). The respective mean A1C changes from baseline to 24 weeks were -1.46 and -1.59% (P = 0.24). A1C <7.0% was achieved by 73.2% (simple algorithm) and 69.2% (carb count) (P = 0.70) of subjects; respective values for A1C <6.5% were 44.3 and 49.5% (P = 0.28). The total daily dose of insulin was lower, and there was a trend toward less weight gain in carb count group patients. Severe hypoglycemia rates were low and equal in the two groups. CONCLUSIONS: Weekly basal-bolus insulin adjustments based on premeal and bedtime glucose patterns resulted in significant reductions in A1C. Having two effective approaches to delivering and adjusting rapid-acting mealtime insulin may increase physicians' and patients' willingness to advance therapy to a basal-bolus insulin regimen.