A 22-year-old male presented with multiple bilateral nodular shadows in the lungs by chest radiograph. He had been asymptomatic and showed no significant abnormal findings in laboratory examinations. He underwent a diagnostic partial lobectomy, and was diagnosed as having primary pulmonary mucosa-associated lymphoid tissue (MALT) lymphoma; i.e. bronchus-associated lymphoid tissue (BALT) lymphoma/BALToma. Neither t(11;18)(q21;q21) chromosomal translocation nor API2-MALT1 chimeric transcript was found at diagnosis. Epstein-Barr virus (EBV) was also not detected in lymphoma cells. He had been a nonsmoker, and had also never shown any associated autoimmune disorders, chronic inflammatory lung diseases or human immunodeficiency virus (HIV) infection. However, he had suffered from moderate atopic dermatitis on his arms from childhood. It appears necessary to clarify whether atopy might play a role in the pathogenesis of API2-MALT1(-) BALT lymphoma for HIV(-) young patients who do not exhibit any other antecedent chronic antigenic stimulations.