The radius of Titan has been determined from Pioneer Saturn observations taken September 2, 1979. The data sets, one in the red (0.64 µm) and one in the blue (0.44 µm), yield radii of 2840 ± 25 km and 2880 ± 22 km, respectively. The discrepancy between the radius values in the two colors is felt to be the consequence of an optically thin submicron haze above the nominal haze layer. The altitude difference between the red and blue limb is 40 ± 20 km. Using a cloud model derived from the Pioneer Saturn data, the lunar occultation radius (Elliot et al., 1975) has been revised to 2845 ± 40 km, in good agreement with the present result. A lower limit of 1.37 g cm⁻³ can now be set on Titan’s bulk density, using the red radius at the haze top. The actual bulk density probably falls in the range 1.65-1.85 g cm⁻³ for an atmosphere of 150- to 250-km thickness below the red limb.