Loop-mediated isothermal amplification (LAMP) is a cost-effective and rapid method for identifying Mycoplasma pneumoniae (MP). We investigated the utility of the LAMP assay in diagnosing MP pneumonia among children in a clinical setting. In this prospective study, the cause of community-acquired pneumonia was evaluated in 111 patients for whom MP was the suspected pathogen. All participants were patients at a city hospital in Japan between April 201 2 and September 2012. Throat swabs for the LAMP assay were obtained at admission, and paired serum samples to measure antibody titres to MP by particle agglutination were obtained at admission and during convalescence. Overall, 45 of 111 (41 %) patients had a fourfold or greater increase in MP titres and received a diagnosis of MP pneumonia. Among them, 43 (96%) patients (median age, 9 years) were positive on the LAMP assay and had a fourfold or greater increase in MP titres. The median interval from fever onset to collection of throat swabs was 7 days (range, 4-10 days). As compared with paired serum titres, the LAMP assay enabled quicker diagnosis of MP (median interval, 13 vs. 7 days), thereby allowing early initiation of appropriate antimicrobial therapy.