Three strains of Cucumber mosaic virus (CMV) have been found to cause a lethal disease, referred to as fern leaf syndromes and mild mosaic symptoms in tomato (Lycopersicon esculentum Mill.) crops grown in Kuwait. CMV strains were detected and identified based on host range, symptomatology, serology, electron microscopy, and ribonucleic acid (RNA) electrophoresis in polyacrylamide gels. A high degree of viral genomic heterogeneity was detected among CMV strains isolated in Kuwait, with no apparent correlation to symptomatology in tomato host plants. Two different virus satellites of "CMV associated RNA 5", designated CARNA 5, were detected in two virus strains that caused both lethal disease and mild symptoms, designated CMV-D1 and CMV-S1 respectively. CARNA5 was not detected in the third CMV strain that caused fern leaf syndromes designated CMV-F. All the three isolated strains were serologically indistinguishable from each other and may belong to one serotype according to Ouchterlony gel diffusion tests. These strains transmitted via aphids (Myzus persicae Sulz) in a non-persistent manner. Physical properties of the virus strains were very similar where thermal inactivation test showed that virus withstood heating for 10 min at 70oC, dilution end point was 10-4, and the longevity in vitro at room temperature was less than 5 days for all virus strains. CMV-D1 and CMV-F were the most devastating diseases spreading in both greenhouse and field-grown tomato where aborted flower buds failed on fruit setting due to the viral infection. This is the first report to isolate three different strains of CMV in Kuwait.