Infection by Cryptosporidium baileyi was first confirmed in red grouse in northern England in 2010 and within three years spread to 48 per cent of moors. These form the last English stronghold for the rarer black grouse, and given the rapid spread of respiratory cryptosporidiosis among red grouse, concern has been expressed about possible infection. In 2010, the authors started screening black grouse for cryptosporidiosis in (1) dead birds taken for postmortem examination, (2) sample birds caught at night and (3) an observational study of birds attending leks. Between 2011 and 2016, five males were sent for postmortem examination, of which three had suspected cryptosporidiosis. No disease was found in one; the second had extensive, subacute to chronic sinusitis; and the third had severe sinusitis and unilateral conjunctivitis. PCR analysis detected cryptosporidial DNA in the third bird only; however, the parasite was not seen in stained preparations or on histopathology. No cryptosporidiosis clinical signs were observed in 69 birds caught at night or in 170 birds attending leks. The authors have no conclusive evidence that cryptosporidiosis is causing sinusitis in black grouse. However, a single positive cryptosporidia PCR result from an affected bird does raise the possibility that they may be infected with the parasite. © British Veterinary Association (unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.