The second-order elastic constants of single-crystal cassiterite, rutile structure SnO2, have been measured as functions of pressure (1 bar to 10 kbar) and temperature 25¿--100¿C) by using the pulse superposition method. The observed negative pressure derivative and positive temperature derivative of Cs=1/2(C11C12) are in qualitative agreement with those measured for isostructural TiO2 <Manghnani, 1969> and GeO2 <Wang and Simmons, 1973>. According to the VRH averaging scheme the pertinent isotropic bulk elastic properties are Kso=2.123 Mbar, (∂Ks/∂P)T=5.50, and (∂Ks/∂T)P=-0.18 kbar/¿C. The calculated bulk modulus Kso of cassiterite is related systematically to the corresponding data for TiO2 and GeO2 with respect to cation radius; however, the pressure and temperature derivatives of Kso for SnO2 are significantly lower and higher, respectively, than those of the rutile structure analogues.