We combine accurate ab initio calculations of the second and third density virial coefficients. B(T) and C(T), of He-4 with measurements of its (p-rho-T) behavior to determine the fourth density virial coefficient D(7) The measurements were made with a two-sinker, magnetic-suspension densimeter at pressures up to 38 MPa. The measurements on isotherms from T = 223 K to T = 323 K were previously published; new measurements from T = 323 K to T = 500 K are presented here On each isotherm, a regression of the virial expansion was constrained to the ab initio values of B(T) and C(T), the regression determined D(T) as well as two apparatus-dependent parameters that compensated for systematic errors in the measurements. The percentage uncertainties of D(T) ranged from 2.6% at T = 223 K to 95% at T = 400 K to 24 7% at T = 500 K, where these uncertainties are expanded uncertainties with coverage factor of k = 2 corresponding to a 95% confidence interval These uncertainties are 1/6th of the uncertainty obtained without the ab initio values of B(T) and C(T) The apparatus-dependent parameters can be used to calibrate the densimeter, and this will reduce the uncertainty of other measurements made with this two-sinker densimeter The new values of D(T) will find applications in accurate gas metrology, such as a primary pressure standard based on the refractive index of helium (C) 2010 Elsevier Ltd. All rights reserved.