The t(11;18)(q21;q21) API2/MALT1 translocation is a specific chromosomal abnormality in extranodal marginal B-cell lymphomas of the mucosa-associated lymphoid tissue (MALT) type, particularly in those occurring in the stomach and lungs. Identification of t(11;18) may aid in the diagnosis of MALT lymphoma and strongly predicts resistance of gastric MALT lymphoma to Helicobacter pylori eradication therapy. We developed a robust real-time reverse transcription-polymerase chain reaction (RT-PCR) procedure to efficiently detect t(11;18) in virtually all types of specimens used in routine diagnostic workups. We blindly tested 40 samples from 38 patients with gastric MALT lymphoma; 10 (25%) of 40 samples, or 8 (21%) of 38 patients were positive for t(11;18). In contrast, t(11;18) was not detected in 8 cases of gastric large B-cell lymphoma, 11 cases of chronic active gastritis, and 16 samples unrelated to lymphoma. Our findings suggest that real-time RT-PCR for t(11;18) may be a valuable tool with much relevance in the current clinical management scheme.