Glioblastoma as second primary malignancy (SPM) has been reported after prostate cancer, meningiomas, Hodgkin's lymphoma. We report an extremely rare case of glioblastoma as SPM, occurring after remission of diffuse large B-cell lymphoma (DLBCL). Fifty-year-old male presented with loss of consciousness followed by right-sided weakness. He was treated with chemotherapy for DLBCL of the cervical lymph nodes, 5 years back. Present scans revealed well-defined intra-axial lesion in the left parietal lobe, suggestive of central nervous system (CNS) involvement by lymphoma. Left parieto-occipital craniotomy was performed and microscopic examination revealed the tumor to be Glioblastoma, WHO Grade IV. The tumor cells were positive for glial fibrillary acid protein and negative for leucocyte common antigen. He was treated by radiotherapy and temozolomide. Pathologic examination is a must for CNS lesions. Had it not been for the biopsy, the patient would have been treated as a recurrence of CNS lymphoma by chemotherapy and would have probably succumbed.