We used morphometric data from 1276 Crocodylus moreletii captured in northern Belize (1992–2001) to develop predictive models for determining body size (total length [TL], snout-vent length [SVL]) from measurements of single attributes (dorsal cranial length [DCL], cranial width [CW], snout length [SL] and width [SW], body mass [BM], rear-foot length [RFL]), quantify sexual size dimorphism, examine ontogenetic changes in cranial morphology, re-evaluate maximum body size attained by this species, and estimate standing crop biomass of crocodiles at our principal study site. Strong positive allometric relationships were found between measures of body length and other morphometric attributes, and provide a reliable means to estimate body length from tracks, skulls, and body parts. The maximum DCL:CW ratio is attained at a relatively small body size and preceded a dietary shift from insects and arachnids to vertebrates and ampullarid snails. The SL:SW ratio of C. moreletii is highly variable and because of overlap with C. acutus, deemed of little value for distinguishing these two sympatric species. Both overall and adult sex ratio (female:male) was male biased and differed significantly from parity. The mean SVL of adult males (98.3 ± 21.3 cm) was significantly greater than that of adult females (87.3 ± 15.9 cm). A compressed sexual size dimorphism index (SDI) of 2.12 was calculated for C. moreletii in northern Belize. Based on skull measurements, the current size record for C. moreletii in Belize is 362 cm TL. Standing crop biomass of C. moreletii at our principal study site (Gold Button Lagoon) was estimated to be 9.5 kg/ha.