The problem of fluorescence in slab geometries is solved exactly and analytically to first order. Analytic expressions, whose direct evaluation should be faster and more accurate than current numerical methods, are derived for differential and integral dose and for differential reflection and transmission coefficients, for the single slab case. The basic expressions are then used to obtain the general solution for the dose profile of the multislab problem. The limitations of the first‐order approximation are discussed and illustrated by comparison with Monte Carlo results. It is found that even in a situation especially chosen to ensure the validity of the first‐order approximation, a Monte Carlo calculation reveals the presence of higher‐order effects.