Two forage sorghum hybrids ( ATx 623 X GL and FS25A) were grown from April 1985 to February 1987 at the Agricultural Experiment Station of the University of Puerto Rico at Lajas, Puerto Rico to determine the influence of maturity stage increases of 10 days (from the 45th to the 85th day) and how the presence and severity of foliar diseases affect the dry forage and crude protein yields. Dry matter content was higher for FS25A (16.1%) than for ATx 623 X GL (14.9%) whereas total yield for dry matter (DMY) was higher for ATx 623 X GL (3.84 t/ha) than for FS25A (3.51 t/ha). Both content and yield of dry matter increased with maturity stage in both genotypes. The sorghum hybrids did not differ significantly in crude protein content (CPC), but crude protein yield (CPY) was higher for ATx 623 X GL (421.6 kg/ha) than for FS25A (358.9 kg/ha). CPC declined with increased plant maturity. Foliar diseases appeared to limit DFY and CPY in both sorghum hybrids. Downy mildew, leaf blight, rust, grey leafspot, and zonate leafspot appeared seasonally. Leaf blight and downy mildew were the most prevalent from January to May, grey leafspot from May to September, and zonate leafspot from September to November. Rust was severe during all seasons.