We present results of single crystal neutron diffraction experiments on La2-xSrxCuO4-δ. The analysis of the temperature dependence of the LaO bond lengths shows that almost the entire thermal contraction of La2CuO4 between 540 K an 50 K is due to the decrease of the LaO9 polyhedron, the CuO bond distances remain almost constant. Doping of La2CuO4 with Sr (or additional O) decreases both CuO bond lengths. The large thermal parameters especially of the apical O indicate the instability of all examined crystals against a second phase transition. © 1991.