Maize (Zea mays L.) in monoculture and in association with bush and climbing beans (Phaseolus vulgaris L.) was evaluated at CIAT in the Cauca Valley, Colombia (1,000 m elevation, 4° N lat). Since small farmers in the Andean zone plant maize at low densities in association with beans, the objectives were to measure the effects of the associated legume crop on maize yields and net returns.Maize yields did not differ significantly between monoculture and associated cropping at harvest densities from 3 to 4 ✕ 104 plants/ha, in trials with different bean cultivars, bean plant densities, planting systems, and relative dates of planting of the two crops. There were no significant differences between systems in the following maize components: ear length, ear and cob diameter, row number, shelling percent, weight per 100 seeds, harvest index, prolificacy index, total biological yield, or plant height. Lodging was less severe in an associated culture of maize, wiht an average of 16.4% in association compared to 28.7% in monocrop over six trials. Less fall armyworm (Spodoptera frugiperda Smith) attack was observed in associated crop maize than in monoculture. Efficiency of land use increased with addition of beans to the system, and highest net income was achieved with associated cropping systems. These results may help to explain why small farmers continue to utilize associated cropping systems in the tropics of Latin America.