© 2016 Polskie Towarzystwo Hematologów i Transfuzjologów, Instytut Hematologii i TransfuzjologiiObjective and importance We present the first case of a precursor acute subdural B-lymphoblastic lymphoma mimicking an acute subdural hematoma. Clinical presentation A 19 year old male presented with an acute onset of headache, nausea and vomiting. CT scan showed crescentic right-sided, frontoparietal subdural mass isointense with cortex and showing homogeneous enhancement after gadolinium. Intervention The patient underwent a craniotomy and a gray subdural tumor with invasion of both dura and brain was observed. The invaded dura was resected and duraplasty performed. Histopathologically, the tumor was composed of small round cells infiltrating soft tissue. In some areas of the tumor, cells were arranged in a linear, “Indian file” fashion between collagen bundles. Their nuclei were generally uniform, round to ovoid in shape, small to medium in size, and featured delicate chromatin. Accompanying cytoplasm was scant. Necrosis was absent. On immunohistochemical analysis, the tumor cells were positive for CD79a, TdT, CD10 and CD34. Conclusion Subdural lymphoma can present as a neurosurgical emergency, and lymphoma should be considered as a rare but possible diagnosis before operation.