Diisodecyl phthalate (DIDP) has been proposed as a suitable reference material for industrial application in the region of moderately high viscosity. The paper reports a new set of viscosity measurements of a 99.5 % GC sample of this substance, which are directly traceable to the primary standard reference value-the viscosity of water at 293.15 K. The present measurements, performed with a vibrating-wire sensor, were carried out at atmospheric pressure over the temperature range (283 to 313) K. Over this temperature range, the viscosity varies from approximately (37 to 267) mPa·s. The measurements have been carried out with an instrument that has already been the subject of improvement since the first measurements were performed, and it relies upon calibration exclusively against the primary standard of viscometry. The estimated overall uncertainty of the results does not exceed ± 1 %, over the whole range of the measurements and, for the results obtained at temperatures in the vicinity of 293 K, is ± 0.8 %. The higher quality of the present measurements, and their direct traceability to the primary reference value for viscosity, justifies the replacement of our earlier set of preliminary data on DIDP viscosity.