The lattice parameter of body centered cubic (bcc) beta titanium was determined as a function of temperature and hydrogen concentration using neutron diffraction, In pure titanium, the lattice parameter a = 0.331 nm at 900 degreesC and the thermal expansion coefficient kappa (T) = 13.8 X 10(-6) degreesC(-1) over the temperature range 900 degreesC to 1000 degreesC, The solution of hydrogen in beta titanium is seen to expand the lattice but it has little effect on the thermal expansion coefficient. The dependence of the lattice parameter on atomic percent hydrogen was found to be linear over the hydrogen concentration range 0 to 30 at.%, as expressed by the hydrogen-induced expansion coefficient K-H = 2.1 X 10(-4) nm/at.%H.