The relationship of duration of illness and severity of neurological impairment to psychometric performance and activities of daily living was examined in 57 patients with Huntington's Disease (HD). As earlier studies suggested, a distinct cognitive profile characterized patients early in the disease. Duration of symptoms, however, proved to be a weaker correlate of cognitive decline than was motor impairment at the time of testing. For predicting adaptive functioning, both duration of symptoms and neurological status were important variables. This study underscores the limitations of length of illness as a classificatory variable in studies of dementia in HD. We further suggest that future studies consider the contribution of defects in precise timing and sequential operations to the cognitive and adaptive deficits of these patients.