Our aim was to evaluate if genetic diversity of Pneumocystis carinii could influence the detection by molecular techniques in bronchoalveolar lavage (BAL) fluids and in non-invasive specimens (induced sputum, oropharyngeal washing and serum/blood). P. carinii is morphologically similar in different hosts although several strains have been identified by biomolecular techniques. Variations of mt-LSU and ITSs sequences could determine a lack of hybridization of some clinical samples and could have diagnostic consequences with loss in sensitivity and specificity of available molecular tests, but at the moment no data support a significant impact of genetic diversity in these sequences on molecular detection of P. carinii for clinical purposes.