This study gives the results of allozyme diversity within and among 20 wild Lima bean populations uniformly distributed throughout the Central Valley of Costa Rica. The electrophoretic analysis of seven enzyme systems show five monomorphic loci and a relatively low level of polymorphism for the other loci. This moderate level of polymorphism is unexpected for a species for which a fair amount of allogamy rates has been reported, at least among the cultivated forms. The genetic parameters (mainly percentage of polymorphic loci, mean genetic diversity, percentage of heterozygotes and fixation index) indicate a tendency for a predominantly selfing breeding system in the wild Lima beans although some values range between selfing and mixed-animal breeding systems. Very low within-population diversity is observed while a good diversity is found among populations. Results also show a departure from Hardy-Weinberg equilibrium on most analyzed populations in the target site This might be due to populations divided into subpopulations among which no natural crosses occur randomly, to weeding practices or to overlap of generations within some populations. All the results obtained in this work are discussed in view of further studies for the planning of in situ conservation in a quickly evolving tropical environment.