Cyclins and cyclin-dependent kinases regulate the cell cycle. Cyclin A has a dual role in cell proliferation. It is essential in the S phase for DNA replication, and it is also involved in G2-M-phase transition, signifying actively dividing cells. The expression of cyclin A was determined by immunohistochemistry in paraffin sections of 126 soft tissue sarcomas. The median cyclin A score was 10.8% (range, 1-54%). Cyclin A expression correlated with the S-phase fraction, Ki-67 score, G2-M phase, and grade. It did not correlate with the size of the tumor. A high cyclin A score predicted a poor metastasis-free survival (P < 0.01) and a poor disease-specific overall survival (P = 0.01). We concluded that the expression of cyclin A is a powerful prognostic factor in soft tissue sarcoma. Moreover, the cyclin A score determines the fraction of tumor cells in the S phase and the G2 phase, which are the most sensitive cell cycle phases for current modalities of cancer treatment.