On-fann trials were conducted during the spring season of 1999 and 2000 to evaluate the yield performance of tomato (Lycopersicon esculentum Mill.) cultivars grown under an organic management system. In 1999, twelve cultivars: 'Bonita', 'Celebrity', 'Colonial', 'Empire', 'Floramerica', 'Joker', 'Liberty', 'Merced', 'Mountain Pride', Olympic', 'Pilgrim' and 'Sunmaster' were grown under an organic management system consisting of mulching with grass straw, fertilizing with cow manure and using organic pesticides for insect control. Similar cultivars were evaluated in spring 2000, but due to lack of seed, 'Bonita' and 'Liberty' were replaced with cultivars 'Keepsake' and 'Mountain Fresh'. In 1999, significant differences (P<0.05) in tomato faiit yield were observed among cultivars. Marketable yield ranged from 28.5 t ha"1 for cultivar 'Pilgrim' to 43.8 t ha"1 for 'Sunmaster'. The top three cultivars with yields of over 40 t ha"1 were 'Sunmaster', 'Bonita', and 'Empire'. 'Sunmaster' also produced the highest total number of tomato fruits (233,000 ha"1). Significant yield differences were also observed in 2000. Marketable fruit yield in 2000 ranged from 20.0 t ha"1 for cultivar 'Olympic' to 38.6 t ha"1 for 'Merced'. The top four cultivars were 'Merced', 'Mountain Pride', 'Sunmaster' and 'Keepsake'. Tomato fruit worm was the major insect pest affecting most cultivars. The organic pesticides used were not very effective in controlling fruit worms. This study indicates that cultivars 'Bonita', 'Empire', 'Keepsake', 'Merced', 'Mountain Pride' and 'Sunmaster' are suitable for tomato production under an organic management system.