Grapevines infected with Tomato ring spot virus (ToRSV) pose an economic risk for growers in the northeastern United States. This study describes a one-step real-time reverse-transcription polymerase chain reaction (RT-PCR) SYBR Green assay for detecting ToRSV in grapevines. Two newly designed primer pairs based on the ToRSV coat protein gene sequence were evaluated for specificity and optimized for a SYBR Green assay. The primer pair ToRSV1f/1r yielded a 130-bp product with strong primer-dimer products, whereas the primer pair ToRSV2f/2r yielded a 330-bp product with weak primer dimer products. Real-time RT-PCR detected ToRSV in more naturally infected grapevines maintained in the greenhouse than did enzyme-linked immunosorbent assay. The nucleotide sequences of the fragments amplified from grapevine growing in Pennsylvania using real-time PCR were divergent from previously published sequences.