The anatomy of the owl monkey (Aotus) retina is reviewed and compared with that of one of its diurnal relatives, the capuchin monkey (Cebus). A mechanism is suggested by which the owl monkey has biased its retinal organization towards a conformation most advantageous far scotopic vision. (C) 2000 John Wiley & Sons, Inc. Col Res Appl, 26, S118-S122, 2001.