Background: Composite tissue allograft recipients require intensive immunosuppression and are therefore at risk of infections. Filamentous fungal infections are among the complications most difficult to manage in organ transplant recipients. Methods: Case report and literature review. Case Report: Two years after bilateral forearm transplantation, a 35-year-old patient presented with a tumor-like lesion on his thigh after a penetrating injury caused by a sliver acquired during hiking. The lesion was excised completely, and microscopic examination revealed a filamentous fungal infection. Alternaria alternata was identified as the causative agent. Induction therapy with liposomal amphotericin B for one week followed by oral itraconazole maintenance therapy for eight weeks was successful, with no signs of recurrence or side effects at 18 months' follow-up. Conclusion: This is the first reported case of invasive A. alternata infection in a composite tissue allograft recipient. The infection was managed successfully with local excision and systemic antifungal treatment.