The extent intraspecific variation among 42 morphological characters within Neoseiulus californicus (McGregor) (Acari : Phytoseiidae) is examined. Neoseiulus californicus is an important biological control agent used commercially worldwide to control pest mites in many crops. The correct diagnosis of this species is thus of prime importance for successful biological control and agricultural development. Incorrect interpretation of intraspecific variation could lead to misidentification and potentially to the description of new species that may be invalid. Three hundred female N. californicus representing ten populations collected from all over the world were measured and compared with the types of two morphologically close species: Neoseiulus marinus (Willmann) and Neoseiulus ornatus (Athias-Henriot). Significant differences between the populations were observed for almost all of the characters considered. However, these differences were small and low within-population standard errors in measurement data were observed. The mites collected in Chile were very different from the specimens of the other populations of N. californicus considered. The level of intraspecific morphological variation found within N. californicus indicates that caution must be applied to correctly determine species boundaries within this genus and morphological variation needs to be considered more in species’ descriptions. Based on our morphological analysis we conclude that N. ornatus, N. marinus and N. californicus are valid species. Redescriptions of these three species are given in this paper.