Morphometric variability was studied in six domestic Venezuelan populations of the blood-sucking bug Rhodnius prolixus Stal 1897 (Reduviidae, Triatominae) and in a sylvatic population identified as R. robustus Larrousse 1927. Evidence is here provided by both uni- and multifactorial analyses of extensive variation of morphological traits between the R. prolixus populations studied. Regardless the geographic or climatic environmental factor tested, none can be retained in a selective model accounting for the morphological variability observed. Moreover, the results failed to support any correlation between the morphological Mahalanobis' distances and geographical distances. The genetic relationships between these populations inferred from the present data, are more consistent with some demic structure, resulting from random genetic drift by founder effects, than with any alternative population genetic model. It is noteworthy that the range of variation of these morphological traits in R. prolixus includes the putative R. robustus population. Therefore, the species-specific status of R. robustus, at the very least the local Trujillo population studied, is questioned. In addition, a preliminary multifactorial analysis bearing on three other Rhodnius relatives, R. pictipes Stal 1872, R. nasutus Stal 1859 and R. neglectus Lent 1954, confirmed the marked morphological differentiation of R. pictipes from all other species and showed a clear morphological differentiation of R. nasutus and R. neglectus both from one another and from R. prolixus.