Patients with myotonic dystrophy (MD) were compared to a control group, matched to the patients in important demographic variables including IQ, on the Sternberg Memory Scanning procedure, to investigate the hypothesis of a selective change in speed of information processing in MD patients. The neuropsychological functioning of these MD patients was also compared to normative data to provide a descriptive picture of their abilities; these results were correlated to the factors of age of onset and duration of the disease. Finally, the MD patients were also compared to the defined control group on the neuropsychological measures. There was little evidence of selective slowness of information processing or particular deficit independent of overall IQ. Neuropsychologically, the MD patients as a group performed at the low average level. There was, however, a wide range of abilities, suggesting that MD patients are not a unitary group in terms of neuropsychological functioning. Age of onset of the disease was important, at least for certain results. Further research of the neuropsychological functioning of MD patients must account for the wide range of results, with more precise measures of actual onset of the disease and muscular weakness, in a longitudinal evaluation.