The Hawaiian Euphorbia is an assemblage of 17 species, seven of which are endangered and four others rare. Euphorbia kuwaleana is an endangered species of small shrubs restricted to three small populations in West O'ahu, Hawai'i. The species has declined to fewer than 1,000 individuals largely due to habitat encroachment by alien plant species and the periodic fires that occur in the vicinity. Genetic variation was assessed among individuals in two populations to determine what impact small population size has had on genetic diversity within the species using RAPD markers. Results demonstrate that polymorphism within these populations is high (mean = 82.5%), equal to or exceeding that of many other nonendangered Hawaiian species. Genetic similarities within (0.741) and among (0.716) populations, F_ST (0.072), and PCO analysis all indicate differentiation among the populations although in close geographical proximity (<1 km apart). Conservation efforts for this species should focus on protection of existing populations from eminent threats and the establishment of new populations in suitable habitats on O'ahu.