The diurnal cycle of liquid water path (LWP) over the subtropical and tropical oceans is examined using two years of TMI satellite microwave radiometer data. Diurnal variations are found to be a considerable fraction of the mean, especially in the regions of extensive low cloud to the west of continents. The mean amplitude of the diurnal cycle in the subtropical low cloud regions is 15-35% of the mean LWP. Early morning maxima in LWP are found throughout most of the subtropics, consistent with a diurnal cycle driven by cloud solar absorption. In deep convective regions of the west Pacific the diurnal cycle is also strong and tends to peak slightly later. Interestingly, the amplitude of the diurnal cycle in the SE Pacific and Atlantic stratus regions is considerably larger than in their northern hemisphere counterparts for as yet unknown reasons. The data provide important constraints for models aiming to simulate the diurnal cycle of clouds.