PURPOSE: The purpose of this study was to determine whether a localized full-thickness eyelid excision results in a proportional decrease in the total number of eyelashes or whether a full complement of visible lashes persists, thus suggesting a compensatory increase in the anagen/telogen ratio among the remaining follicles. METHODS: A retrospective chart review was performed on 38 patients who underwent full-thickness eyelid resections repaired with primary eyelid closure for either benign or malignant eyelid lesions. Demographic and surgical data were collected, postoperative eyelid photographs were reviewed, and eyelashes were counted. RESULTS: There were 10 upper eyelids and 28 lower eyelids in 10 men and 28 women, with an average age of 57.9 years (range, 14-86 years). The lesion pathology was benign in 21 cases (55%) and malignant in 17 cases (45%). The full-thickness defect involved <25% of the eyelid in 16 cases (42%) and >25% of the eyelid in 22 cases (58%). The follow-up period ranged from 50 to 319 days, with an average of 94 days. In contralateral controls, upper eyelids had an average of 72.1 lashes and lower eyelids had an average of 38.2 lashes, and there was no statistical significance between men and women. In lower lids that underwent <25% resection, control lids had an average of 37.3 lashes and operative lids had 37.1 lashes. In lower lids that underwent >25% resection, control lids had an average of 38.7 lashes and operative lids had 34.2 lashes. This represents an 11.6% decrease and was statistically significant. In upper eyelids that underwent <25% resection and >25% resection, control eyelids had an average of 74.9 lashes and 69.3 lashes and operative eyelids had 77.6 lashes and 69.1 lashes, respectively. Finally, lash count was compared by benign versus malignant pathologic diagnosis. In upper eyelids with benign lesions and malignant lesions, control eyelids had an average of 73.8 lashes and 65.3 lashes and operative eyelids had 74.6 lashes and 68.3 lashes, respectively. In lower eyelids with benign pathology and malignant lesions, control eyelids had an average of 34.5 lashes and 41.4 lashes and operative eyelids had 33.8 lashes and 36.8 lashes. This represents an 11.1% decrease and was statistically significant. CONCLUSIONS: Full-thickness excision of eyelid margin tissue including lashes does not usually affect postoperative lash numbers. Because the total number of follicles is reduced, the percentage of lashes in the anagen versus the resting or telogen phase apparently increases compared with the preoperative state. This eyelash study contributes to the growing body of literature on the poorly understood topic of hair follicle cycle regulation.