BackgroundDermatophytosis (ringworm) caused by members of theTrichophyton mentagrophytescomplex is rarely diagnosed in pigs but has been recognized as an increasingly common infection in humans. Further, resistance to antifungal drugs have been reported both in Asia and in Europe. This is the first scientific report of infection by theT. mentagrophytescomplex in pigs in the Nordic countries.Case presentationSkin lesions developed in grower pigs in an organic fattening pig farm with outdoor production and following laboratory analyses, dermatophytosis caused by members of theT. mentagrophytescomplex was diagnosed. Infection was linked to poor hygiene, high humidity, and moderate outdoor temperatures, in combination with high pig density. A farm worker developed a skin lesion after close contact with affected pigs, which highlighted the zoonotic potential of porcine dermatophytosis. The dermatophytes may have originated from the herd supplying the growers where similar lesions occurred in pigs. Further, pigs from another organic fattening herd that received growers from the same supplier herd also developed dermatophytosis. The lesions healed without treatment as the housing conditions were improved. Isolation of affected pigs prevented spread to other pigsConclusionMembers of theT. mentagrophytescomplex can cause ringworm in pigs. The fungi probably persist in the haircoat and may cause overt disease when environmental conditions promote growth of mycelia.