This retrospective analysis describes confirmed cases of MPX virus infection observed at four sexual health centers in London.  Demographic and clinical characteristics, and sexual history information, were retrieved from patient records and an internal sexual health dashboard.  Confirmed cases all had laboratory-detected infection via an in-house, pan-orthopoxvirus RT-PCR assay.  Between May 14 and May 25, 2022, MPX was confirmed in 54 individuals (among 4500 patients seen): all were MSM (2 identified as bisexual).  96% were unaware of having been in contact with a known case.  Median time between reported symptom onset and testing was 7 days, and median time between symptom onset and last sexual contact was 2 days.  24% were people living with HIV, all of whom were receiving cART with CD4 > 500 cells/mm³.  85% had plasma RNA < 50 copies/mL within the previous 90 days, and 15% had viral loads between 200-500 copies/mL (these individuals had recently initiated cART after a new HIV diagnosis).  95% of HIV-negative patients were taking PrEP.  All individuals presented with skin lesions, although presentation varied according to stage of MPX infection.  Over two-thirds endorsed at least one recent systemic symptom such as fever, fatigue/lethargy, or myalgias prior to lesion onset: most systemic symptoms were mild and lasted less than three days.  94% presented with at least one lesion in the genital or perianal area.  Lymphadenopathy (usually inguinal) was present in 56%.  Lesions were noted in more than three sites in 22% HIV-negative individuals compared to 54% PWH (authors indicate no other relevant clinical differences were observed between these groups).  Five required admission due to evolution of genital or perianal lesions into coalescing ulcerations (one had disseminated infection), many with superimposed cellulitis requiring antibiotics and analgesia (one person received tecovirimat)—all reported intense pruritus at the start of the eruptive phase.  Median length of hospital stay was 7 days.