The molecular structure of propargylgermane, HCCCH2GeH3, has been determined by gas-phase electron diffraction. The electron-diffraction investigation has been supported by density functional theory and ab initio calculations. The ra value of the bond lengths (pm) are: r(C–Ge)=197.2(1); r(C–C)=143.9(2); r(CC)=123.1(1); r(H–Cacetylene)=108.5(3); r(C–H)=111.6(3) and r(Ge–Haverage)=153.7(2). The Ge–C–C angle is 111.7(1)° and the C–CC angle is 178.3(4)°. The uncertainties are one standard deviation from the least-squares refinement.