Previous studies of experimentally induced colds and influenza have shown that sleep is impaired during these illnesses. This has been observed for both subjective reports and polysomnographically recorded sleep. The present study investigated whether naturally occurring illnesses influenced sleep measured using actimetry. Twenty-two volunteers had their sleep recorded on two occasions approximately 14 days apart. On the first occasion 15 of the volunteers had a cold and the other 7 were healthy. On the second occasion all volunteers were healthy. No significant differences were found between the healthy and colds group for any of the actiwatch measures. However, the numerical trends suggested that those with colds had lower sleep efficiency. Significant correlations were found between nasal symptoms and sleep disturbance. Reported fatigue the next day was also associated with less efficient sleep. These results confirm that the common cold can have detrimental effects on sleep but suggest that the overall magnitude of the effect is small and that it may reflect nasal obstruction.