We present the results of quantitative forward modeling of the Sardinian rifted margin of the Tyrrhenian Sea. The purpose of this study is to investigate the thermo-mechanical structure that affects the thinning of the lithosphere across the margin. The role of lithospheric necking during basin formation, constrained by basement topography, Moho depth, and gravity anomalies, is modeled for different compensation models. Independent constraints are obtained from the analysis of the predicted thermal structure. A deep level of necking (25 km) is required to explain the observed crustal geometries and gravity anomaly signature. The model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning. Prerift lithospheric conditions, strain rate, and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the Tyrrhenian Sea. A forward model for basin stratigraphy is presented for the polyphase history of the Tyrrhenian rifting. This model provides quantitative estimates of time-space dependent crustal thinning and rates of extension. ¿ American Geophysical Union 1995