A probable case report of an abdominal botryomycosis has been hypothesized in a patient with a stable HIV infection under an effective antiretroviral therapy. Hyperpyrexia, abdominal pain and tenderness, and a thickening of small intestinal walls associated with multiple mesenteric adenopathies and a peritoneal involvement, prompted an ultrasonography-guided fine needle biopsy, and later a laparoscopy-laparotomy which excluded a neoplastic or lymphoproliferative disorders, showing only abundant fibrotic and necrotic-steatonecrotic tissue, with sparse multinuclear giant cells type Langhans. The prompt response to surgical intervention and a treatment with i.v. meropenem alone might be referred to a concurrent gram-negative infection of abdominal origin, until a late culture of an atypical Mycobacterium came to our attention over one month after the end of hospitalization. An updated literature search is presented and discussed, in relationship with the observed, extremely infrequent case reports of botryomycosis in different clinical settings.Keywords: Intrabdominal mass; Peritoneal involvement; Inflammatory signs; Surgical treatment; Meropenem; Botryomycosis; Atypical mycobacteriosis Una "misteriosa" massa intraddominale a eziologia infettiva, in un paziente con infezione da HIV controllata. Un "ritardo diagnostico" consente di approfondirne la conoscenza studiando una patologia rara CMI 2011; 5(3): 95-106