Dispersal plays a crucial role in a range of evolutionary and ecological processes; hence there is strong motivation to understand its evolution. One key prediction is that the relative beneﬁts of dispersal should be greater when dispersing away from close relatives, because in this case dispersal has the additional beneﬁt of alleviating competition with individuals who share the same dispersal alleles. We tested this prediction for the ﬁrst time using experimental populations of the opportunistic pathogen Pseudomonas aeruginosa. We measured the ﬁtness of isogenic genotypes that differed only in their dispersal behaviors in both clonal and mixed populations. Consistent with theory, the beneﬁt of dispersal was much higher in clonal populations, and this beneﬁt decreased with increasing growth rate costs associated with dispersal.