Bean (Phaseolus vulgaris) is one of the most important vegetables in Sri Lanka. In 1999, a new bean disease was reported from the town of Balangoda. Symptoms included a bright yellow mosaic pattern on the leaves, rugosity, reduced leaf size and stunting of the entire plant. Depending upon the time of infection, plants either produced fewer flowers and pods or none at all. Since its discovery, the disease has spread to most bean-growing areas of the island. In 2009, six samples showing symptoms were collected from different districts of Sri Lanka for viral analysis. All were tested by ELISA for Tomato spotted wilt virus, Impatiens necrotic spot virus, Cucumber mosaic virus (CMV), Southern bean mosaic virus, and with broad-spectrum antisera for potyviruses and begomoviruses. One sample tested positive for potyviruses and another for CMV; all tested positive for begomoviruses. All samples gave portions of DNA-A and B of a bipartite begomovirus; a Blast search of the GenBank database revealed high sequence identity to Horsegram yellow mosaic virus (HgYMV). HgYMV has been identified in India where it was found to infect various legumes: bambara groundnut, French bean, groundnut, lima bean, mung bean, pigeon pea, soyabean and horse gram. All cultivated bean cultivars are susceptible and the disease is regarded as the most serious threat to bean production in Sri Lanka. Using the current taxonomic nomenclature, the name Horsegram yellow mosaic virus-[Sri Lanka:2009] HgYMV-[LK:09] for this variant of the virus is proposed. This is thought to be the first report of the virus in Sri Lanka.