A survey was conducted in Qazvin province in the North of Iran, to determine the incidence of tomato viruses including: Tobacco mosaic virus (TMV), Tomato yellow leaf curl virus (TYLCV), Tomato chlorotic spot virus (TCSV), Tomato bushy stunt virus (TBSV), Tomato spotted wilt virus (TSWV), Tomato ring spot virus (ToRSV), Tomato aspermy virus (TAV), Potato virus Y (PVY), Beet curly top virus (BCTV), and Cucumber mosaic virus (CMV). A total of 742 tomato symptomatic samples were collected during the summer of 2007 in five regions of Qazvin province (Qazvin, Takestan, Boeen-Zahra, Alborz and Abiyek) and tested by enzyme-linked immunosorbent assay (ELISA). TSWV was detected in Alborz (4.4 %) and Abiyek (3.57%) regions but TMV and CMV were detected in all five regions. The greatest and least incidence of tomato viruses were recorded in Alborz (40.7 %) and Takestan (11.1 %), respectively. The presence of these viruses was also evaluated in the weed hosts as natural sources of plant viruses. The greatest and least incidence of tomato viruses in weed hosts were recorded in Boeen-Zahra (25.6 %) and Qazvin (12.8 %), respectively. TSWV was not detected in weeds. Transmission tests demonstrated that Thrips tabaci acts as TSWV carrier and Myzus persicae and Aphis gossypii were CMV carriers. Seed transmission tests were positive for TMV (13 tomato seedlings from 100 seedlings), but no TSWV transmission was observed through the seeds of infected tomato fruits
