Both RAMSIS and MADYMO are widely applied for computer aided vehicle design. Both programs are used to simulate occupant-vehicle interactions where RAMSIS focuses on ergonomics in normal driving conditions and MADYMO focuses on passive safety in impact conditions. This paper describes simulations of human seat interactions using RAMSIS and MADYMO.An interface has been developed to convert RAMSIS human models and postures to MADYMO. Static seat interaction was first simulated using RAMSIS. This provided an estimated posture and a qualitative assessment of comfort. Then the posture as estimated by RAMSIS was analyzed in MADYMO. The seat was modeled in MADYMO as an arbitrary surface, and the combined surface compliance of seat and human tissues was defined in terms of stress versus penetration. The MADYMO analysis of the posture estimated by RAMSIS provided for instance joint loads, seat contact pressures and seat friction. Since the RAMSIS posture and the MADYMO seat model are based on fundamentally different approaches, the posture predicted by RAMSIS does not provide exact equilibrium of the body on the seat in the MADYMO simulation. An equilibrium body position close to the RAMSIS position could be found using MADYMO equilibrium analyses. Thus realistic seated body positions and postures can be defined as starting point for dynamic simulations like impact analysis or for dynamic comfort analysis.