Dahlia is an important ornamental crop in the U.S. The economic value of the crop is often affected by viral diseases. Of several viruses that infect dahlia, dahlia mosaic virus (DMV) is of most concern. However, little or no information is available about its distribution. A survey of dahlias in several states in the U.S. was carried out during 2003 and 2004. Samples from CA, GA, MD, ME, MT, NM, PA, OR, and WA were tested for DMV. To develop a molecular detection assay, the viral genome was cloned and sequenced and based on the sequence information, DMV-specific primers were used in a PCR-based assay. DMV was detected in >90% of the samples tested. Based on the detection of DMV, a wide range of symptoms were found to be associated with DMV infection. A real-time PCR assay was adapted for rapid detection of DMV. Considering its widespread occurrence, steps are needed to limit its further spread. An effective intervention program would include use of virus-free material to minimize its impact. Availability of a rapid and sensitive detection method such as the once described should facilitate not only production of virus-free dahlias but elimination of virus infected material from breeding and propagating stocks. This is the first report of a survey to determine the extent of DMV incidence in dahlias.