A study in 50 children suffering from acute brucellosis demonstrated that acute arthritis is a common and often predominant manifestation of the disease. The patients lived in an area where brucellosis is endemic: their ages ranged from six months to 12 years. All patients had a brucella agglutination titer of greater than or equal to 1:320 on admission. The knee and hip joints were most commonly affected with symptoms and findings from only one joint predominating. Associated findings of only moderately elevated ESR and normal leucocyte counts with relative lymphocytosis in the vast majority of the cases made it fairly easy to distinguish acute brucella arthritis from septic arthritis of other origin. A positive blood culture for Brucella melitensis was obtained in 35 of the patients. Treatment with tetracyclines, trimethoprim-sulphamethoxazole, with or without combination with streptomycin, resulted in a prompt recovery in all patients. No mortality was seen. Seven patients were readmitted with reinfections during a mean follow-up period of 13 months. Two patients with a history of prolonged fever, malaise and arthralgia were found to have osteomyelitis of the adjacent bone tissue. They also recovered without sequelae.