A constant volume apparatus has been used to measure the vapor pressure and single phase densities (PVT) for 1,1,1-trifluoroethane (R143a), an ozone friendly refrigerant. The sample has a purity greater than 99.91% by mass. The measurements were done from 244 to 365 K at pressures up to 4.4 MPa and at densities ranging from 5% to 99% of the critical density. The uncertainties involved in the measurement of temperature, pressure, mass, volume, and specific volume are explicitly given. Thirty-three values for the vapor pressure and sixty-three densities along six isochores are presented and have been compared with previously published data and correlations. A Wagner type correlation for the vapor pressure and a Martin-Hou equation of state have been used to fit the measured data, which have been analyzed using the average absolute deviation, bias, and standard deviation. The gas phase densities have been used to determine the second virial coefficients.