In this paper, a theory of "clumps" in drift-wave turbulence is developed, based on the stochastic treatment of trajectories developed by Misguich and Balescu. It is shown that there exists a clump effect in a magnetized turbulent plasma as well as in an un-magnetized one. The existence of this effect makes the actual diffusion across the magnetic field much smaller than the diffusion predicted by Dupree's theory. Ah explicit expression for the clump life-time is derived this life-time is proportional to the diffusion (across magnetic field) characteristic time and depends logarithmically on the initial relative position of particles.