The major ultrastructural features of the sperm tail differentiation in the lizard, Acanthodactylus boskinus (A. boskinus) have been described. The initial step is the caudal migration of the centrioles followed by insertion of the proximal centriole in the nuclear fossa and extension of the distal centriole to form the microtubular axoneme. Thereafter, tail differentiation involves the development of neck region and middle, main and end pieces. The later three tail pieces along their extension encompass the axonemal complex which reveals the typical (9+2) arrangement of microtubules. The axonemal complex in the middle piece is enveloped within two successive sheaths, the mitochondrial and fibrous ones while its extension in the main piece is only encircled by the fibrous sheath. The end piece only manifestes the existence of the axonemal complex surrounded by the plasmalemma of the fully differentiated spermatids.