The viscosity of seven (0.062, 0.166, 0.456, 0.552, 1.754, 3.062, and 4.700) mol center dot kg(-1) binary aqueous NaI solutions has been measured with a capillary-flow technique. Measurements were performed at pressures up to 30 MPa. The range of temperature was from ( 298 to 575) K. The total uncertainty of viscosity, pressure, temperature, and composition measurements was estimated to be less than 1.6 %, 0.05 %, 15 mK, and 0.015 %, respectively. The effect of temperature, pressure, and concentration on viscosity of binary aqueous NaI solutions was studied. The measured values of the viscosity of NaI(aq) were compared with data, predictions, and correlations reported in the literature. The viscosity data have been analyzed and interpreted in terms of the extended Jones-Dole equation for the relative viscosity (eta/eta(0)) of strong electrolyte solutions to accurately calculate the values of the viscosity A- and B-coefficients as a function of temperature. The derived values of the viscosity A- and B-coefficients were compared with the values calculated from the Falkenhagen-Dole theory and ionic B-coefficient data, respectively. The physical meaning parameters V and E in the Eyring's absolute rate theory of viscosity, the hydrodynamic omolar volume V-k(effective rigid molar volume of salt) in the extended Einstein relation for the relative viscosity, and the Arrhenius-Andrade parameters A and b = E-a/R (where E-a is the flow activation energy) were calculated using the present experimental viscosity data. The effective pressures P-e due to the salt (NaI) in water were calculated from the present viscosity measurements by using the TTG model. The predictive capability of the various models for viscosity electrolyte solutions has been tested.