Cucumber mosaic virus (CMV) has been detected in lentil(Lens culinarisL.) seed grown in New Zealand. In 1994 experimental plots of lentil plants ‘Rajah’ inoculated with CMV yielded 15% less seed than uninoculated. In 1995, seed losses were similar for ‘Rajah’ and ‘Titore’, but losses were greater at 17 and 19%, respectively. Plant numbers were also reduced by CMV infection—by 18% in ‘Rajah’ and 7% in ‘Titore’. Thousand seed weight was not affected by infection. Surveys of commercial lentil seed lines detected CMV incidences of between 0.05 and 2.5%. In a field experiment in 1996, using four levels of seed‐borne CMV (0, 0.5, 1, and 2%) obtained by blending infected and healthy seed, mean seed‐borne incidences in harvested material of between 1.5 and 6% were recorded. No reductions in seed weight or subsequent germination rate were recorded. Plant numbers were slightly reduced by seed‐borne CMV. Transmission of CMV from infected seed was measured. A linear relationship was observed from 1% transmission in plots sown with clean seed to 4.9% transmission in plots sown with seed having a 2% level of infection.