This study addressed the effect of mother-infant bed-sharing on infant body temperature and possible mediating mechanisms. Axillary temperatures were recorded for the entire night in 26 infants on both a bed-sharing night and a solitary sleeping night, accompanied by polysomnography and video-taping to allow assignment of sleep stages and behavioral analysis. All infants were approximately 3 months old, healthy, Latino and breast-feeding; 16 of the infants bed-shared since birth while the others routinely slept alone. Bed-sharing was associated with a significantly increased mean axillary temperature compared to solitary sleeping in both routine bed sharers and routine solitary sleepers. This increase was expressed only in non-REM sleep, with no differences during REM sleep or waking. The increase in temperature during bed-sharing may be related to an increased frequency of transient, movement-associated arousals during bed-sharing.