Larval polytene chromosome banding patterns of Simulium (Simulium) eximium de Meijere, 1913 collected from West Java and Sumatra in Indonesia were observed and a standard map was presented. This species had three chromosome pairs which were numbered I-III in decreasing order of size. Each centromere of all chromosomes was distinguished by an expanded region with heterochromatin. A haplotype involving two distinctive heterochromatic bands in the centromere (21A) and section 20B of the chromosome I was heterozygous in most of the males from the population of Puncak (West Java) and appeared to be sex-linked. The differences in chromosomal polymorphism, coupled with those in sex-related banding, suggest that two sibling species exist in the S. (S.) eximium morphospecies, one in Puncak (West Java) and the other in Danau Ranau (South Sumatra).