Achondroplasia is the most common form of human skeletal dysplasia, with an incidence between 1/15.000-1/77.000. It is a dominant autosomic disorder, with complete penetrance and with more than 80% of the cases result from sporadic and recurrent mutations, associated with increased paternal age. Recently, a missense mutation (G380R) located in the transmembrane domain of the FGFR3 was found to account for more than 95% of patients studied. In order to characterize the mutations involve in this dysplasia in an Argentine Achondroplastic population, 21 sporadic cases and 2 unrelated familial forms were randomly selected from 80 patients followed up in our Hospital. The patients showed the typical physical and radiological features of this dysplasia. The G→A transition (responsible for 98% of the G380R substitutions) was analyzed by PCR of exon 10 and allele specific oligonucleotide hybridization using the following primers: Nor: 5′-AGCCCACCCCGTAGCTGAG-3′; Mut: 5′. CTCAGCTACAGGGTGGGCTT-3′. This mutation was present in 21 of 23 chromosomes studied. The other 2 chromosomes were positive for N540K substitution, previously associated with Hypochondroplasia. The prevalence of G380R (95.5%) found in our achondroplastic population was in agreement with previous reports regarding other populations. The presence of N540K mutation in patients with achondroplastic fenotype shows a wide range of fenotypic variability associated with this substitution.