I'd like to add that there isn't always a clear cut delineation between the types. For example, MODY is highly penetrant, heritable diabetes that fits neither classification. The idea that type 1 == genetic and type 2 == external is really no longer the prevailing view. The better description is the production of insulin where in type 1, there is a lack of insulin production and typically in type 2 insulin resistance (and possibly deficient insulin). The causative factors are complex and a combination of genetics and environmental factors. I'm a type 2 diabetic with none of the traditional risk factors (typical diet, and underweight), from a family with a high diabetes frequency (sister and father).