The long-term behavior of photoluminescence (PL) of porous silicon (PS) at room temperature (RT) and elevated temperatures was investigated in order to assess the suitability of PS for commercial applications, which mostly require lifetimes of years. At higher storage temperatures (60-120 degrees C) the decay time t(1) of PL intensity is between 1.8 and 0.4 h. Surprisingly after approximately 20 days of storage at high temperature the PL intensity recovers to a steady-state value of quantum efficiency QE = 2%, which is also approached when stored at room temperature. By oxidizing the samples the QE is increased (to approx. 3%). From the extremely slow decay of PL after recovery, a decay time constant of t(3) approximate to 2000 days was estimated. For samples, that are permanently irradiated by UV light (1.5 mW/cm(2)), the decay time is shorter. Hence, with intermitting UV radiation lifetimes of years can be expected.