Field observations were made on the relationship between sex and density and the attachment sites of Hyalomma aegyptium to its major host, the tortoise Testudo gracea. The usual sites of attachment were around the back legs and tail of the host. For undamaged hosts there was a positive correlation between tick density and the numbers of each sex attaching away from these usual sites of attachment. More females were attached to the front of the host than males. For damaged hosts no correlation between attachment site and density was found, although more females than males were found at the front of the host. Females attaching to the carapace or plastron fractures had a higher mortality. Hyalomma represents the third genus of ticks with reptile hosts which shows sexual differentiation in attachment sites. The attachment sites of parasites to their hosts are usually quite specific (Halvorsen, 1976; Whitfield, 1979) with survival of the parasites being maximized at their normal attachment site. Any changes in attachment site, for whatever cause, reduce parasite survival and/or reproduc-