Individuals who sleep poorly report spending more time mind wandering during the day. However, past research has relied on self-report measures of sleep or measured mind wanderingduring laboratory tasks, which prevents generalization to everyday contexts. We used ambulatoryassessments to examine the relations between several features of sleep (duration, fragmentation,and disturbances) and mind wandering (task-unrelated, stimulus-independent, and unguidedthoughts). Participants wore a wristband device that collected actigraphy and experience-sampling data across 7 days and 8 nights. Contrary to our expectations, task-unrelated andstimulus-independent thoughts were not associated with sleep either within- or between-persons(n = 164). Instead, individual differences in unguided thoughts were associated with sleep dis-turbances and duration, suggesting that individuals who more often experience unguided train-of-thoughts have greater sleep disturbances and sleep longer. These results highlight the need toconsider the context and features of mind wandering when relating it to sleep