Studies of the growth of GaSb self-assembled islands on GaAs and their morphological evolution for varying GaSb coverage are presented. Islands had a mean height of 15 nm and planar dimensions of 60 by 130 nm. Evolution of the island height, width and length shows that the island height and width increases rapidly in the first 2 s and then stabilizes, while the island length increases linearly. This behavior is interpreted using the theory by Tersoff and Tromp [Phys. Rev. Lett. 70, 2782 (1993)]. The volume growth was found to be initially faster than bulk growth.