The transient elongational viscosity and molecular orientation are measured for a TLCP under simple uniaxial elongational flow. Substantial strain hardening is observed for Hencky strains greater than one, with both the molecular order and transient elongational viscosity becoming independent of strain rate. The transient elongational viscosity is observed to follow a master curve in this regime, scaling as strain squared. X-ray scattering measurements of the orientational order parameter show the strong orienting ability of elongational flows. The quantitative results are compared to those of simple shear flow, as well as to molecular theories, showing important deviations from the behavior expected for model, rigid rod nematics.