The two-spotted spider mite (Tetranychus urticae Koch) is an important pest of tomato (Lycopersicon esculentum Mill.) crops in temperate regions as this spider mite has a very large capacity for population increase and causes severe tomato yield losses. There is no described tomato cultivar fully resistant to this pest, although resistant accessions have been reported within the green-fruited tomato wild species L. pennellii (Corr.) D’Arcy and L. hirsutum Humb. & Bonpl. We observed a L. pimpinellifolium (Jusl.) Mill. accession, ‘TO-937’, which seemed to be completely resistant to mite attacks and we crossed it with the susceptible L. esculentum cultivar. ‘Moneymaker’ to obtain a family of generations consisting of the two parents, the F1, the F2, the BC1 to L. esculentum, and the BC1 to L. pimpinellifolium. This family was evaluated for mite resistance in a polyethylene greenhouse using an experimental design in 60 small complete blocks distributed along 12 double rows. Each block consisted of five F2 plants in one row and one plant of each of the two parents, the F1, the BC1 to L. esculentum, and the BC1 to L. pimpinellifolium in the adjacent row. Plants at the 10–15 leaf stage were artificially infested by putting on them two pieces of French bean leaf heavily infested with T. urticae. After two months, evaluations of infestation were made by visual observation of mite nets and leaf damage. Plants that were free of signs of mite reproduction on the top half were considered as resistant, plants with silky nets only on their basal leaves, intermediate, and plants with mite reproduction on both basal and top canopies were scored as susceptible. Dominance for resistance appeared because all the ‘To-937’, BC1 to L. pimpinellifolium, and F1 plants were resistant. Not all ‘Moneymaker’ plants behaved as susceptible because 35% of plants were intermediate. In the BC1 to L. pimpinellifolium and the F2, most plants were scored as resistant, only 7 % BC1 and 3 % F2 plants were intermediate, and a single F2 plant (0.3 %) was susceptible. With these figures, resistance seemed to be controlled by either four or two genes according to whether segregation in the BC1 or in the F2, respectively, were considered. These results could in part be explained because of appearance of negative interplot interference due to the high frequency of resistant genotypes within most of the generations. Therefore, the family was evaluated again but using a different experimental design. In the new experiment, 16 ‘TO-937’, 17 ‘Moneymaker’, 17 F1, 37 BC1 to L. pimpinellifolium, 38 BC1 to L. esculentum, and 125 F2 plants were included. Each of these test plants was grown besides a susceptible ‘Moneymaker’ auxilliary plant that served to keep mite population high and homogeneous in the greenhouse. Negative interplot interference was avoided with this design and all the ‘TO-937’, F1, and BC1 to L. pimpinellifolium plants were resistant, all ‘Moneymaker’ test plants were susceptible, and 52 % BC1 to L. esculentum and 25 % F2 plants were susceptible, which fitted very well with the expected for resistance governed by a single dominant gene. The simple inheritance mode found will favour sucessful introgression of mite resistance into commercial tomatoes from the very close relative L. pimpinellifolium.