We quantified sexual size dimorphism, reproduction, and diet in the flap-necked chameleon, Chamaeleo dilepis, using museum specimens. Females were larger than males in both snout-vent length (SVL) and pelvic width. The smallest sexually reproductive female was 80 mm SVL, whereas the smallest mature male was 60 mm. Female body size also correlated with clutch size (mean: 44.2, range: 19–74) and volume, suggesting the female-biased size dimorphism may be the product of fecundity selection. Males and females have slightly asynchronous reproductive cycles but breed during spring–summer. Chamaeleo dilepis feeds on a range of arthropods, but their diet is dominated both numerically and volumetrically by orthopterans, followed by coleopterans.