A stable decagonal quasicrystal phase in the Al–Mn–Pd system is described. Its composition is Al70·5Mn16·5Pd13, as determined by X-ray microanalysis attached to a scanning electron microscope. The temperature range of stability has been found to be around 800°C by investigation of differently annealed specimens in a transmission electron microscope. An icosahedral quasicrystal phase with composition Al70·5Mn8·5Pd21and a face-centred icosahedral quasilattice has also been found, partly in coexistence with the new decagonal phase. The icosahedral phase is also stable at temperatures around 800°C. The Al–Mn–Pd system is the first system in which stable decagonal quasicrystals as well as stable icosahedral quasicrystals occur.