To the Editor:— The clinician, who finds two or more uncommon and seemingly unrelated diseases in the same person, may wonder if the concurrence is simply coincidental or has larger significance. Should one of the diseases be of unknown origin, recognition of the association may provide clues to its etiology. Thus, case reports linking certain congenial cytogenetic disorders with leukemia suggest that chromosomal defects are involved in leukemogenesis.1 We recently observed chronic granulocytic leukemia developing in a patient with myotonic dystrophy, a genetically determined disease not previously described with leukemia. Report of a Case:— A 47-year-old woman was admitted to the National Cancer Institute in October 1967 with the diagnosis of chronic granulocytic leukemia. Evaluation revealed massive splenomegaly, a leukocyte count of 302,000/cu mm, and bone marrow studies showing granulocytic hyperplasia and the Philadelphia chromosome. She also had far-advanced myotonic dystrophy, with characteristic facies and muscle weakness, cataracts bilaterally, and