The definition of a horizontal stabilizer is constrained by a large number of criteria. Some of those are purely mission related (overall dimensions, weight, tail boom folding etc.) and are external inputs as far as aerodynamicists are concerned; however, most of them are related to helicopter flight mechanics. The high speed characteristics throughout the whole weight/CG range and the dynamic stability advocate for a large size stabilizer. On the contrary, the pitch-up phenomenon due to the interactions between the main rotor and the stabilizer in the low speed envelope asks for a reduced area, and this point is all the more important in a Navy helicopter during deck landing when the pilot workload can be drastically increased with large nose-up attitudes. Special attention was paid to the compromise regarding horizontal stabilizer size during the NH90 helicopter definition phase. The dynamic stability criterion, made less stringent by the choice of a Fly-by-Wire control system, as well as high speed were addressed with the Eurocopter simulation model. This model has little predictive capability as regards low speed pitch-up behavior. Tests were thus conducted in the DNW wind tunnel with a large scale powered model while taking advantage of an existing Mach scaled rotor. These helped derive the low speed trim characteristics of the NH90 helicopter. Both analytical and experimental studies oriented the stabilizer configuration choice for the first flight in December 1995. One year later, the predicted characteristics were confirmed by the flight tests results. This paper covers the whole development procedure, from the theoretical calculations and wind tunnel experiments to the flight tests data validation.