Hepatosplenic T-cell lymphoma is rare, and most cases that have been reported with cytogenetic abnormalities have an isochromosome 7q with or without trisomy 8. A 7-year-old boy who had hepatomegaly and splenomegaly was diagnosed with hepatosplenic T-cell lymphoma on the basis of a bone marrow biopsy. The karyotype of the lymphoma cells at diagnosis included a ring chromosome 7 and trisomy 8. Fluorescence in situ hybridization analysis with chromosome 7 probes demonstrated amplification of a 7q31 sequence in the ring chromosome. While isochromosome 7q is a common abnormality in hepatosplenic T-cell lymphoma, and other structurally abnormal chromosomes 7 have been reported in a small number of cases, this is the first reported case of ring chromosome in hepatosplenic T-cell lymphoma.