Styrene is a known mutagen and suspected carcinogen, used in the reinforced plastic industry. This study aims to identify the occurrence of DNA single strand breaks (SSBs) in workers exposed to styrene levels far below the recommended standards. We compared 26 exposed workers with 26 control subjects and found a significant increase in the incidence of DNA-SSBs in the exposed individuals. The levels of the biological indices of exposure (urinary mandelic and phenyl glyoxylic acids) were less than 25% of the recommended limits. Reduction of the threshold limit values/time-weighted-average (TLV-TWA) applied is strongly recommended.