Onion thrips, Thrips tabaci Lindeman, is one of the most serious pests of onion throughout the world. Knowledge of spatial distribution is important for developing an effective sampling plan and ultimately for IPM strategies for a given pest. In the present study spatial distribution of T. tabaci was studied on onion, Allium cepa L. under three irrigation regimes of Egypt during 2021. Dispersion index like a variance to mean ratio (σ²/X) revealed a negative binomial distribution, whereas the other dispersion indices like David Moore index (IDM = σ²/X-1), mean crowding (X*), Lloyd's mean crowding index (X*/X) and ‘k' of negative binomial verified the aggregated nature of the spatial distribution of onion thrips at 10, 20 and 30-days irrigation intervals throughout the cropping season. Moreover, Taylor's power equation was σ²= 1.549X^1.581, σ²= 1.636X^1.623 and σ²= 1.872X^1.504, while Iwao's patchiness regression equation was X^*= 2.973+1.432X, X^*= 9.251+1.457X and X^*= 9.161+1.352X for the three above-mention irrigation intervals, respectively. An optimum number of required samples varied with the mean density of the thrips.