Cladding ovalities or localized oval regions in the cladding have been observed in many advanced liquid-metal fast breeder reactor fuel elements. The occurrence of ovalities can be related to an internal fuel element mechanism, and in particular to a localized nonaxisymmetric fuel-cladding mechanical interaction resulting from fuel cracking and rearrangement. Elastic calculations of the cladding shape in the vicinity of an ovality have been performed using a simplified model of the fuel-cladding mechanical interaction. A comparison between the calculated and measured ovality shapes shows good agreement. The size of ovalities as measured at room temperature has also been related to the size at operating conditions. Both membrane and bending stresses that are associated with ovalities have been calculated. Ovalities observed in advanced fuel elements increase in size with increasing burnup, but are independent of cladding thickness, gap size, and peak linear power. Data from a pair of similar elements with annealed and cold-worked cladding may indicate a significant inelastic deformation associated with ovalities.