It has been shown that an all solid-state porous silicon electroluminescent device with an efficiency greater than 0.1% can be fabricated (A. Loni et al., Electron. Lett., 31 (15) (1995) 1288-1289). However, one important factor limiting the practical application of this device is the stability of the electroluminescence. With the support of optical, electrical and chemographical investigations, we report on the factors which might affect the stability of the device, such as operating environment, choice of contact materials, localised electrical breakdown, contact diffusion and the surface passivation of the porous silicon. For devices fabricated with semi-transparent gold contacts, it is shown that the gold is permeable to air and device degradation correlates with oxidation of the porous silicon when operated in air. Devices fabricated with less permeable indium tin oxide contacts are shown to be significantly more stable in air. The degradation of devices with indium tin oxide contacts does not correlate with oxidation, diffusion of contact material or localised electrical breakdown. However, the degradation is accompanied by the loss of surface hydride passivation from the porous silicon.