To observe the effect of helium and temperature on void formation in aluminum, high-purity foils were irradiated with 1.2- or 1.4-MeV Al+ ions at temperatures from 30 to 120°C, both with and without preinjected helium. Dislocation loops formed in all samples, but the samples without helium produced no voids visible in the transmission electron microscope even after doses up to 2.7 displacements per atom (dpa) (6.5 x 1015 Al+/cm2). Samples preinjected with 0.1, 1, and 10 appm helium and then irradiated at 100 and 120°C produced voids at doses of ∼0.5 dpa (1.2 x 1015 Al+/cm2). With irradiation at 75°C and below, voids formed only in samples preinjected with 0.1 appm helium. With irradiation at 100°C, the average void sizes and void densities were not significantly different for the three helium levels, whereas at 120°C the average void size decreased with increasing helium content and the density increased. With helium levels of 0.1 and 1 appm helium, varying the temperature produced an increase in void size with increasing temperature and a decrease in void density.