Aims: Legionella isolation from environmental samples is often difficult because of the presence of heterotrophic-associated bacteria that frequently overgrow when using standard culture (ISO 11731, 1998; NF T90-431, 2003) methods. To improve Legionella pneumophila recovery from complex water samples (water from cooling towers, biofilms), we evaluated an immunomagnetic separation (IMS) assay using a monoclonal antibody raised against the lipopolysaccharide of Leg. pneumophila sg1 in combination with culture. Methods and Results: This study was conducted on 51 environmental specimens. The comparison between IMS-culture and standard culture (ISO 11731, 1998; NF T90-431, 2003) methods was made using ISO 17994, 2004 criteria for establishing equivalence between microbiological methods based on the upper and lower (X(H) and X(L)) values of the relative difference (95% confidence limit) and D as maximum acceptable deviation (value of the confidence limit). Conclusions: We found that the average performance of IMS culture was higher than the reference method. Significance and Impact of the Study: Thus, this IMS-culture assay is particularly well adapted to the detection of Leg. pneumophila sg1 in environmental samples with high levels of interfering microflora.