This paper proposes a new approach to model the spread of HIV/AIDS among in
travenous drug users (IVDUs). The focus is on a group of n IVDUs within whi
ch infective contacts occur, and which evolves in discrete time, subject to
group splitting, immigration, and emigration. We are interested in finding
the probability distribution of the ultimate number Y-n of HIV infectives
produced by the group as time tends to infinity, and obtain a stochastic re
cursive equation for it. Although, or the surface, the process resembles a
branching process, our results cannot be obtained using techniques from the
theory of branching processes. We use the probability metrics approach to
obtain limit theorems for the normalized sequence L-n = (Y-n - EYn)n(-1/2).
Finally, we consider the behavior of L-n under different sets of regularit
y conditions, when for example L-n = (Y-n - EYn)n(-1/alpha) tends to an alp
ha-stable distribution. (C) 2000 Elsevier Science Ltd. All rights reserved.