ALK-negative anaplastic large cell lymphoma (ALCL) is a peripheral T-cell lymphoma that usually involves lymph nodes or extranodal sites. Leukemic phase of ALK-negative ALCL is exceedingly rare and often carries a poor prognosis. Androgenic steroids have gained popularity among the young, and at higher doses, it can result in immune dysregulation and may be potentially carcinogenic. Case presentation: A 30-year-old gentleman of Malay ethnicity presented to the hematology department with night fevers, loss of weight and bony pain for the past 6 weeks. He is a gymnasium instructor with a history of chronic usage of intramuscular testosterone enanthate. Physical examination revealed ecchymosis over the left elbow and hepatomegaly. A complete blood count depicted anemia, thrombocytopenia and leucocytosis. An 18-Fluorodeoxyglucose positron emission tomography (18-FDG PET/CT) imaging showed a hypermetabolic anterior mediastinal mass of 6.8 × 7.0 × 6.5 cm with diffuse hypermetabolism in the liver, spleen and axial skeleton. The bone marrow trephine and mediastinal tissue histology were consistent with leukemic ALK-negative ALCL. He was treated with CHOEP (cyclophosphamide, doxorubicin, vincristine, etoposide, prednisolone) induction chemotherapy in which he required intensive antibiotic and blood support. He progressed with worsening B symptoms and new diffuse lymphadenopathies suggesting rapid dissemination of the disease. He subsequently succumbed to multiorgan failure with disseminated intravascular coagulopathy at the intensive care unit. Conclusion: Leukemic phase ALK-negative ALCL often carries a complex karyotype and requires early intensive polychemotherapy. Use of anabolic steroids depletes the ability of defending lymphocytes to remove tumour producing cells.