In this report we describe the cases of two siblings with reactive arthritis (ReA) induced by pharyngeal infections. The patients were a man and his sister living with their parents. He developed arthritis in August 1997, and his younger sister developed similar symptoms in September 1998. Their disease conditions were both severe and required hospitalization. Their conditions improved with the administration of nonsteroidal anti-inflammatory drugs together with antibiotics, and both fully recovered within 1-2 weeks. Rheumatic fever was ruled out since streptococcal infections were not demonstrated with antistreptolysin O (ASO) or antistreptokinase (ASK) titers, or with pharyngeal culture. The sister suffered from a rash which was similar to erythema nodosum on her lower extremities, but neither chorea nor carditis was observed. Both human leukocyte antigen (HLA) typing analyses revealed positive results for HLA-B40 and -B39 for the brother and sister, respectively. Both HLA-B40 and -B39 are considered to be related to HLA-B27-negative ReA, most likely poststreptococcal reactive arthritis (PSRA). Therefore, the two patients were tentatively diagnosed as suffering from PSRA.Key words Group-A streptococcal infection · Human leukocyte antigen (HLA)-B27, 39, 40 · Human leukocyte antigen (HLA) typing · Reactive arthritis (ReA)