Acute, non-traumatic joint complaints during childhood can be caused by conditions which require a quick and adequate recognition and treatment as well as by conditions in which an expectant policy can be pursued. On the basis of certain data from the anamnesis, supplemented with findings from the physical examination it is often possible to arrive at a (probable) diagnosis. An algorithm was designed, the differential steps of which were: fever, C-reactive protein titre, involvement of the hip joint, the presence of extra-articular manifestations and the results of a full blood count, erythrocyte sedimentation rate and imaging techniques. When this algorithm was retrospectively applied to the disease data of 115 children with acute, non-traumatic joint complaints, for whom the diagnosis in the status was taken as the gold standard, the correct diagnosis was established for every single child: for 98 (85.2%) by the shortest route and for 17 (14.8%) indirectly. In the case of 4 children, use of this algorithm would have led to unnecessary laboratory investigations and/or treatment. None of the diseases requiring immediate treatment were missed.