Turbulent, single-phase forced convection of water in circular microchannels with diameters of 0.76 and 1.09 mm has been investigated. The data show that the Nusselt numbers for the microchannels are higher than those predicted by traditional large channel correlations. Based on the data obtained in this investigation, along with earlier data for smaller diameter channels, a generalized correlation for the Nusselt number for turbulent, single-phase, forced convection in circular microchannels has been developed. The diameter, Reynolds number, and Prandtl number ranges are 0.102-1.09 mm, 2.6 x 10(3)-2.3 x 10(4), and 1.53-6.43, respectively. With a confidence level of greater than 95%, differences between experimental and predicted Nusselt number values are less than +/-18.6%.