- Background It is not mandatory to report Pediculosis capitis and Phthirus pubis in most countries; therefore, little is known about the seasonality of these infestations. Methods We analysed the data based on routine and mandatory reporting of every case of Pediculosis capitis and Phthirus pubis to the Army Health Branch Epidemiology Department, Israel, over the last two decades. Results The average 20-year incidence of Pediculosis capitis shows a significant rise during the warmer months (R2 = 0.692, P < 0.05) with a parallel significant decrease in the cooler months (R2 = 0.893, P < 0.05). The results for Phthirus pubis show a significantly higher person-time incidence in the winter (P < 0.001). Sensitivity analysis to investigate possible sources of heterogeneity during this time indicated that no single year was an important source of heterogeneity. ConclusionsPediculosis capitis is more frequent in the warmer months, whereas Phthirus pubis is more dominant in the cooler months.