A variable length encoding method for encoding a finite or infinite series of values corresponding to a random variable whose distribution monotonically decreases on either side of the mean value in which the encoding tree has a regular structure which is defined by an arithmetic and logic device. In order to encode each value E, a first binary word, including only bits having a same value and whose number of bits B is an increasing function of the value to the encoded E, is determined. The number of bits B is computed according to a predetermined arithmetic and logic function B(E). The method also involves determining a second binary word having a value to be encoded, in the set of values to be encoded arranged in order of decreasing probability, and whose number of bits B' is derived from the function B(E) and from the number of bits B in the first binary word. A code word is formed by combining the first and second binary words thus determined.