Eighteen yam (Dioscorea spp.) cultivars from five species were evaluated for yield and severity of mosaic, anthracnose, and black leafspot (Curvularia spp.). Plantings were established at Mayagüez and Isabela, Puerto Rico, in the 1985-86 and 1986-87 growing seasons. Severe mosaic was found on D. trifida (Mina), which was the lowest producing cultivar both seasons. Five cultivars of D. esculenta (Kombi, Seti, Doli, Muni, and Beti) showed moderately severe mosaic symptoms in 1985-86, and black leafspot symptoms in 1986-87. Among these cultivars, Doli produced the highest tuber yields, 21,000 kg/ha (9.4 tons/acre). Among D. alata cultivars, differences in anthracnose were related to genotype, location, and season. Leon Globe and Forastero were the most susceptible and lowest yielding cultivars. Gunung produced the highest yield, a maximum of about 40,000 kg/ha (17.9 tons/acre). It was least affected by anthracnose, with less than 15% defoliation in November. Tuber yields in D. alata cultivars were highly associated with anthracnose severity ratings (r = —0.81 * *) . Both seasons more anthracnose was found in Isabela than in Mayagüez. Anthracnose was more severe in 1986-87 than 1985-86.