A double-grid avalanche counter (DGAC) with an active area of 13 × 13 cm 2 is described. It is position sensitive in two dimensions with a resolution of about 1.0 mm. A 100% detection efficiency was obtained simultaneously for fission fragments and α-particles of a 252Cf source with pentane at 4 Torr gas pressure. This pressure is a compromise regarding both detection efficiency and time resolution. The timing properties were investigated for α-particles and fission fragments as a function of the gas pressure and distance between the electrode wires. For fission fragments the time resolution measured with 50 μm wires corresponds to an intrinsic time resolution of the DGAC of ∆t < 150 ps. No significant differences were obtained for 20 and 50 μm anode wires. The avalanche width in the DGAC was investigated for different gas pressures. For fission fragments the energy loss resolution amounts to 20%. No position dependent timing shift was observed.