This study deals with fiber deformities in thirteen cultivars of Egyptian cotton, namely: Giza 45, Giza 70, Menoufi, Giza 68, Giza 76, and Giza 77 of the long-staple category, Giza 67, Giza 69, Giza 75, and Dandora of the long-medium-staple category, and Giza 66, Giza 72, and Ashmouni of the medium staple category.The cotton fiber deformities were classified major and minor according to their frequency. The major fiber deformities included thin fiber, knee, knot, small spur, and large spur, whereas the minor fiber deformities included forked and protuberant fibers. Difference in number of fiber deformities among the studied cultivars, types of fiber deformities, and the interaction between number and type of fiber deformities differed statistically.Fiber deformities occurred in about ½ to 2/3of the developing neps, ensuring their troublesome role in the cotton textile industry. Neps were classified into groups according to number of fiber deformities associated with each, in order to evaluate the role of fiber deformities in neppiness.