A high-resolution, finite-difference numerical study is made of three-dimensional natural convection in a cubical enclosure. The two vertical sidewalls of the enclosure are differentially heated. An internal partition of varying size and shape is located at the mid-plane of the cavity. Comprehensive numerical solutions to the time-dependent Navier-Stokes equations are acquired by using a control volume-based computational procedure. Two Rayleigh numbers, 10(7) and 5 x 10(9), are considered for the enclosure filled with air ( Pr = 0.71). The salient three-dimensional flow characteristics are illustrated for two selected types of the partition geometry. The results clearly demonstrate the prominent three-dimensional features in the partitioned enclosure. Elaborate numerical visualization efforts have been conducted, and both the flow and thermal fields are portrayed in sufficient detail. The effects of the partition geometry on the three-dimensional flow properties are scrutinized.