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Background: Myotonic dystrophy type 2 (DM2) is a recently discovered adult muscular dystrophy. Similar to DM1, this disease causes progressive debilitating weakness, clinical myotonia, and early cataracts and is thought to cause widespread physiologic dysfunction of multiple organ systems., Objective: To analyze and compile the laboratory abnormalities of patients with DM2., Design: Baseline DM2 laboratory data were compiled representing 68 different types of laboratory tests and 1442 total studies., Setting: University medical center., Patients: Eighty-three adults with genetically confirmed or clinically probable DM2 were identified. Of these patients, 49 had documented baseline laboratory screening., Main Outcome Measures: The individual frequencies of abnormal laboratory values in the population with DM2 studied., Results: Of the 1442 studies, results for 359 (24.9%) were outside of their standard reference ranges. Of the 68 types of laboratory tests studied, 43 had values from 15 or more different patients with DM2. The relative frequency of an abnormally elevated laboratory value was greater than 50% in several tests, including the levels of creatine kinase, total cholesterol, lactate dehydrogenase, and alanine aminotransferase. In addition, serum levels of IgG were low in 75% of all patients with DM2 tested, and absolute lymphocyte counts were low in 54% of all patients with DM2 tested., Conclusions: There is a high frequency of laboratory abnormalities in patients with DM2. These abnormalities provide insight into the widespread pathologic manifestations of DM2 and may form a basis for clinical monitoring and disease screening.