Neoplasia in porcupines is rarely reported in the literature, and the prevalence is unknown. A retrospective review of records from a private zoo diagnostic pathology service found four cases of mammary adenocarcinoma in Indian crested porcupines (Hystrix indica) from four separate zoological institutions. All cases presented in geriatric females (14–19 yr of age) as freely movable subcutaneous masses within the mammary chain. None of the individuals had additional clinical signs, radiographic, or hematologic changes at initial presentation. All cases were managed with surgical excision in the form of either an excisional biopsy or a partial mastectomy. Histologic examination diagnosed all tumors with anaplasia and moderate to high numbers of mitotic figures. Two cases required subsequent surgeries for management of local recurrence in the years following initial diagnosis. One case is 19 months postsurgical removal without evidence of metastasis or local recurrence. Two of the cases were euthanized after diagnosis of inoperable metastases to the lungs and spinal cord, including one previously treated with an oral nonsteroidal antiestrogen medication, tamoxifen. The third case was euthanized due to degenerative mobility changes and renal dysfunction and had no evidence of metastasis. The average survival time from initial surgical excision to euthanasia for the three applicable cases was 33 months. These cases suggest that surgical excision alone may result in temporary management of mammary adenocarcinoma in this species. Metastasis can occur, and routine screening with advanced imaging may aid in early detection of these lesions.