A systematic study was performed to examine the frequency of columbid circovirus (CoCV) infection in diseased young pigeons submitted for necropsy and its relevance to pigeon health. Existing diagnostic methods were compared. Among 176 diseased young pigeons examined, CoCV infection was detected in 83 cases using negative contrast electron microscopy. Histopathological examination allowed a clear diagnosis in only 42 pigeons. Therefore, a polymerase chain reaction assay and an in situ hybridization test were developed as additional diagnostic tools. CoCV is by far the most frequently detected infectious agent in diseased young pigeons. Infected pigeons reveal a broad range of concurrent infections. Pathological findings suggest an immunosuppressive effect of CoCV.