The viscosity of the dilute phase of a 3He-4He solution has been measured using a vibrating wire viscometer situated in the mixing chamber of a dilution refrigerator. The viscosity was extracted from the damping of the resonator for temperatures between 3.7 mK and 100 mK. In the low-temperature Fermi liquid regime ηT2=48×10−9 N sec m−2 K2. For temperatures less than 100 mK, the viscometer is a useful secondary thermometer that is not strongly dependent on the applied magnetic field.