Synovial sarcomas are aggressive malignant soft tissue tumors typically observed in adolescents and young adults. They are often characterized by the chromosomal translocation t(X;18)(p11.2;q11.2), which results in the expression of SYT-SSX fusion transcripts. We describe the first case of synovial sarcoma observed in a human fetus. The tumor occurred in the left upper arm and led to intrauterine fetal demise during gestational week 31. Grossly, the tumor measured 10 x 8 x 8 cm, appeared pinkish in color, and developed in the soft tissues of the left arm surrounding the humerus. Histologically, this large tumor showed a dense proliferation of homogeneous spindle cells with some necrotic areas. The positive detection of the SYT-SSX1 fusion transcripts with reverse-transcription polymerase chain reaction in formalin-fixed and paraffin-embedded tissue confirmed the synovial sarcoma diagnosis.