Synovial sarcoma in children below the age of 10 years is rare. We report on three cases of synovial sarcoma which were diagnosed in three children aged 3, 8 and 8 years, respectively. These tumors were located in the hip of the 8-year-old, the foot of the 3-year-old, and the elbow of the other 8-year-old. Histologically, one tumor was a biphasic synovial sarcoma, and the other two, which had been initially diagnosed as infantile fibrosarcoma, were of the monophasic fibrous type. In the three cases, a reverse transcription-polymerase chain reaction (RT-PCR) using ribonucleic acid extracted from formalin-fixed, paraffin-embedded tissues detected SYT-SSX1 fusion gene transcripts resulting from translocation t(X;18)(p11.2;q11.2), which is specific for synovial sarcoma. ETV6-NTRK3 fusion gene transcripts that result from t(12;15)(p13;q25), which is characteristic of congenital/infantile fibrosarcoma, were not demonstrated. In conclusion, other pediatric soft tissue sarcomas, such as congenital/infantile fibrosarcoma, spindle cell rhabdomyosarcoma, leiomyosarcoma and malignant peripheral nerve sheath tumor, should be distinguished from synovial sarcoma in children, especially the monophasic fibrous type. RT-PCR analysis is a useful approach to the final diagnosis of synovial sarcoma arising at such an early age.