The deuterium spin relaxation of fluorene-d(10) (5 mol %) in Licristal Phase 5 has been studied between -15 and +63 degrees C at 15.4, 38.4, 55.3, and 76.8 MHz. The deuterium NMR spectra of the four magnetically distinct deuterons in fluorene-d(10) were recorded as a function of temperature, and the molecular orientational order parameters of fluorene-d(10) were determined from the quadrupolar splittings. The longitudinal relaxation times, T-1z and T-1Q, were measured by the Jeener-Broekaert pulse sequence, and the spectral densities of motion, J(1)(omega(0)) and J(1)(2 omega(0)), for each deuteron were calculated from T-1Q and T-1Z. Above 30 degrees C all four J(2) are frequency independent and only J(1) of the deuterons at the 2,7 and 9,9’ positions show a distinct frequency dependence. At lower temperatures all eight spectral densities are frequency dependent and ail, except J(1) at 15.4 MHz, go through a maximum. The experimental data have been interpreted-partially-in terms of rotational diffusion of an asymmetric top in a uniaxial restoring potential according to the theoretical treatment recently developed by Tarroni and Zannoni (J. Phys. Chem. 1991, 95, 4550). At high temperatures this model gives good fits to the experimental values of the J(M)(M omega(0)), as long as contributions from director fluctuations are added to J(1)(omega(0)) for the 2,7’- and 9,9’-deuterons. At lower temperatures, J(1)(omega(0)) and J(2)(2 omega 0) show a more pronounced frequency dependence than predicted from the rotational diffusion model, indicating that the collision rate of fluorene with the surrounding solvent molecules approaches it reorientation rate. Accordingly, we modified the rotational diffusion spectral densities to reflect the presence of slowly fluctuating torques as proposed by Polnaszek and Freed (J. Phys. Chem. 1975, 79, 2283). The modified spectral densities of motion provide a significantly better fit to the experimental data throughout the nematic temperature region.