The origin of a ring chromosome in a monophasic synovial sarcoma of the diaphragmatic pleura of an 18-year-old man was investigated using spectral karyotyping (SKY) and fluorescence in situ hybridization (FISH). Conventional cytogenetic analysis revealed the following clonal karyotypic abnormalities: 47,Y,t(X;18)(p11.2;q11.2),t(11;19)(q12;q13.4),+12,-13,+r[6]. The SYT-SSX1 fusion transcript was detected with reverse transcriptase-polymerase chain reaction analysis. SKY analysis suggested that the ring chromosome was composed of material from chromosome 8. Subsequent FISH analysis with a whole-chromosome 8 paint probe confirmed the SKY results. This study demonstrates the usefulness of SKY as an adjunct for determining the chromosomal composition of ring chromosomes.