We report the case of a 59-year-old woman who developed rapid-onset type 1 diabetes associated with a marked increase in anti-glutamic acid decarboxylase antibody titer (317.5 U/ml), mild increase in HbA1c level (6.8%), diabetic ketoacidosis, and cytomegalovirus enterocolitis. She was a heterozygote for HLA class II DRB1*0901-DQA1*03-DQB1*0303, and she had HLA class I A24, which may have contributed to the rapid beta cell destruction. Based on the putative molecular mimicry of GAD65 by cytomegalovirus antigen, we hypothesize that the type 1 diabetes in this case was associated with cytomegalovirus infection.