A design of a robust computer control system for balancing and improving the steady-state performance of a triple inverted pendulum-cart system is considered. The controller is based on discrete-time H-infinity theory and is implemented via a robust reduced order dynamic observer. An integrator is used to eliminate the effects of small constant sensor offsets and rail inclinations. Disturbance attenuation and relative stability characteristics are studied via frequency response analysis. Simulation and experimental results are reported.