We describe an 86-year-old male who developed CD20-negative pyothorax-associated B cell lymphoma 64 years after he had suffered from tuberculous pleuritis. Therapy with 8 courses of THP-COP at 2-week intervals was followed by involved-field radiotherapy of 30 Gy. Uncertain complete remission was achieved. Thereafter, local recurrence of pyothorax-associated lymphoma (PAL) at the primary site was seen. The patient received salvage radiotherapy of 50 Gy. The patient died of pneumonia during a second uncertain complete remission. The progression-free survival and overall survival of this patient were 10 and 15 months, respectively. When compared with the median survival of 9 months reported in the literature, the adverse effect of CD20 negativity on prognosis may not apply to PAL patients with an occasional aberrant phenotype.