Most cells in the retina and lateral geniculate nucleus (LGN) of primates have a concentric center/surround receptive-field organization. Details of the relationship between center and surround often can be used to predict how cells respond to visual stimuli. Models of the receptive-field organization and center/surround relationships also are useful when comparing cell classes. In the present study, we used the difference-of-Gaussians (DOG) model to quantitatively examine and compare the receptive-field center/surround organization of koniocellular (K), magnocellular (M), and parvocellular (P) LGN cells of owl monkeys. We obtained estimates of receptive-field center size (r(c)) and center sensitivity (K(c)), and surround size (r(s)), and surround sensitivity (K(s)) from 62 K, M, and P LGN cells by fitting their spatial-frequency responses with a DOG function (Rodieck, 1965; Croner & Kaplan, 1995). The DOG function not only accounted for the responses of P and M cells, but also provided a good description of K-cell responses. We found that at matched eccentricities of less than 15 deg, K cells had the largest r(c) and r(s) among the three cell classes. K cells also had the lowest K(c) and K(s). Center and surround sizes tended to increase with retinal eccentricity for all three cell classes, but K cells showed a more variable pattern. There was an inverse relationship between sensitivity and size for both the receptive-field center and surround in all three cell classes. The surround/center volume ratio remained similar across cell classes. We conclude that K, M, and P LGN cell classes differ in the details of their receptive-field structure, but share common principles of center/surround organization.