We present growth studies of InAs nanowires nucleated from lithographically positioned Au seeds on InAs (111)B substrates. The nanowires are grown in a chemical beam epitaxy system and exhibit high aspect ratios and high homogeneity in length and width. Investigations of wire growth rate as a function of diameter, density, and time were performed and the results indicate that 80% of the growth is due to In species diffusing from the (111)B substrate surface. Furthermore, we have established that the diffusion length on the {110} wire side surfaces exceeds 10 μm. We also observe a decreasing length growth rate with increasing wire diameter.