During annual nest monitoring of Marsh Harriers on the salt marshes of the Dutch Wadden Sea island of Schiermonnikoog, a nestling Marsh Harrier with skin lesions on tarsus and toes was ringed. The skin was flaky and the toes seemed to have nodules with crusts, looking like scabies. Based on pictures (Fig. 1) it was provisionally diagnosed as avian pox. Six days after ringing the nest was visited again to record further developments. By then the leg’s skin seemed to have improved, but affected skin and crusts were also found on the beak (not noticed during the previous visit, but not specifically looked for). Two older near-fledglings in the nest (both males) showed no skin aberrations. After studying the photographs, a veterinary pathologist was unable to unambiguously diagnose the affection as avian pox (only possible to detect via microscopic examination of the skin). Avian pox infections have been reported for several bird of prey species, mostly among those kept in captivity, but never – as far as a search in the literature revealed – for harriers.