Abstract Objective To characterise the clinical features of monkeypox infection in humans. Design Descriptive case series. Setting A regional high consequences infectious disease centre with associated primary and secondary care referrals, and affiliated sexual health centres in south London between May and July 2022. Participants 197 patients with polymerase chain reaction confirmed monkeypox infection. Results The median age of participants was 38 years. All 197 participants were men, and 196 identified as gay, bisexual, or other men who have sex with men. All presented with mucocutaneous lesions, most commonly on the genitals (n=111 participants, 56.3%) or in the perianal area (n=82, 41.6%). 170 (86.3%) participants reported systemic illness. The most common systemic symptoms were fever (n=122, 61.9%), lymphadenopathy (114, 57.9%), and myalgia (n=62, 31.5%). 102/166 (61.5%) developed systemic features before the onset of mucocutaneous manifestations and 64 (38.5%) after (n=4 unknown). 27 (13.7%) presented exclusively with mucocutaneous manifestations without systemic features. 71 (36.0%) reported rectal pain, 33 (16.8%) sore throat, and 31 (15.7%) penile oedema. 27 (13.7%) had oral lesions and 9 (4.6%) had tonsillar signs. 70/195 (35.9%) participants had concomitant HIV infection. 56 (31.5%) of those screened for sexually transmitted infections had a concomitant sexually transmitted infection. Overall, 20 (10.2%) participants were admitted to hospital for the management of symptoms, most commonly rectal pain and penile swelling. Conclusions These findings confirm the ongoing unprecedented community transmission of monkeypox virus among gay, bisexual, and other men who have sex with men seen in the UK and many other non-endemic countries. A variable temporal association was observed between mucocutaneous and systemic features, suggesting a new clinical course to the disease. New clinical presentations of monkeypox infection were identified, including rectal pain and penile oedema. These presentations should be included in public health messaging to aid early diagnosis and reduce onward transmission.