It has been reported that excessive intake of sugar-containing soft drinks results in diabetic ketoacidosis (DKA) or ketosis (DK) in obese patients with non-insulin dependent diabetes mellitus (NIDDM). We describe the clinical characteristics and results of long-term follow-up for 24 newly-diagnosed patients with acute-onset NIDDM presenting with DKA or DK. A history of excessive intake of sugar-containing soft drinks was found in 19 (Group A); serious non-diabetic illnesses were found in 5 (Group B). The range of patient ages in Group A was 16 to 57 years while all patients in Group B were 60 years or older. In Group A, no patient was positive for autoantibodies, specific HLAs for Japanese insulin dependent diabetes mellitus, or mutation of the beta-3-adrenergic receptor gene. The body mass indices (BMIs) at onset and admission and serum C-peptide immunoreactivities at admission and discharge were significantly higher in patients in Group A than in patients Group B. In conclusion, we reconfirmed that excessive intake of sugar-containing soft drinks is one of the contributing factors in DKA or DK-onset NIDDM patients. We found no autoimmune mechanism involved in the pathogenesis and that a polymorphism in the beta-3-adrenergic receptor gene could be associated with the development of soft-drink ketosis.