According to the ADA Nutrition Recommendations and Principles for People with Diabetes, people with diabetes should follow the same guidelines for use of alcohol as anybody else.

The effect of alcohol on blood glucose levels depends on the amount of alcohol drunk and on its relationship to food intake. Alcohol is not metabolized to glucose; if it is consumed without food by people using insulin or oral glucose-lowering drugs, it can cause hypoglycemia - long before blood alcohol reaches levels that would be considered 'intoxicated'. Used in moderation and with food, alcohol doesn't affect blood glucose levels when diabetes is well controlled. For those people using insulin, 1 or 2 alcoholic beverages (see box) can be taken with and in addition to the regular meal plan. ADA cautions that no food should be omitted because of the possibility of hypoglycemia. When calculating calories from alcohol as part of the total caloric intake, it's best to substitute alcohol for fat exchanges (1 beverage = 2 fat exchanges) or fat calories.

1 alcoholic beverage =  -12 oz beer  -5 oz wine  -1 ½ oz distilled spirits

People with other medical conditions such as pancreatitis, dyslipidemia (especially elevated triglycerides), or neuropathy should reduce or eliminate alcohol use.

Source:  ADA Position Statement. Nutrition Recommendations and Principles for People with Diabetes Mellitus. Diab Care 12(Suppl 1), Jan. 2000.