The adult sex-ratio of a widespread dynastine beetle characterized by remarkable sexual shape dimorphism, Phyllognathus excavatus (Forster, 1771), is reported herein for the first time with regards to the Italian populations. These beetles were studied in a coastal locality of Mediterranean central Italy (Latium), and showed a significantly female-biased sex ratio (4.2 females for each male), with a daily sex-ratio fluctuating from equality to 7:1 towards females. Comparisons are presented with sex-ratios of other dynastine beetles studied elsewhere.