The aim of this study was to determine whether wrist actigraphy could be used to assess the daytime effects of stimulant medication in the treatment of narcolepsy. Nine subjects with narcolepsy/cataplexy (medicated and unmedicated) were compared with matched control subjects. Data were collected over 4 days in the subjects' home. It was found that the actigraph variable of Immobility (mean duration of periods of no activity) could be used successfully to differentiate medicated and unmedicated phases, correctly classifying 89% of cases. Narcolepsy subjects differed from controls on Immobility both when medicated and unmedicated. During the unmedicated phase the self-reported nap duration was longer and more naps (3.94 naps) were taken. However, the frequency of naps was still high when medicated (2.43 naps). During the unmedicated phase narcolepsy subjects reported more negative mood states (profile of mood states, POMS) than control subjects. However, with the exception of Vigor, scores on the individual mood factors were within the normal range. Total POMS scores were highly correlated with the actigraphic measure of Movement for both narcolepsy conditions as well as controls, with negative mood associated with less movement. It was concluded that the actigraphy variable of Immobility is sensitive enough to detect treatment effects. The relationship between mood and motor activity warrants further investigation in both clinical and non-clinical populations.