Background:Pyoderma gangrenosum is estimated to occur in 5% to 12% of ulcerative colitis patients. Primary CD30+ cutaneous large cell lymphoma is the second most common cutaneous lymphoma. It may coexists with mycosis fungoides.Main observations: We report a 38-years-old female patient with 12 year history of ulcerative colitis, treated previously with 5-aminosalicylic acid and systemic corticosteroids. The disease has been in remission for the past 1.5 years, with no maintenance treatment. The patient then developed a rapidly progressing ulcerated lesion clinically simulating pyoderma gangrenosum. Physical examination revealed also a small number of hairless hypopigmented patches on the upper and lower limbs which she claimed to have appeared 4 years ago. Surprisingly a histological evaluation of the ulcer revealed a CD30+ primary cutaneous large cell lymphoma, while histology of hypopigmented lesions revealed mycosis fungoides, patch stage. T-cell receptor gene rearrangement from the two lesions didn't reveal the same T Cell clonalitiy and the patients lymphoma was stable.Conclusion:Our case presents the rare coexistence of primary mycosis fungoides and primary CD30+ cutaneous large cell lymphoma, rather than the CD30+ cutaneous large cell lymphoma developing from mycosis fungoides. This case also presents the development of a pyoderma gangrenosum-like lesion of CD30+ cutaneous large cell lymphoma in a patient with ulcerative colitis. An observation that emphasizes the need for a high index of suspicion in cases diagnosed as pyoderma gangrenosum based solely on clinical appearance.