Legionella longbeachae was cultured from the sputum of a patient suffering from Legionnaires' disease. Source identification efforts included analysis of samples of potting soil from the patient's garden, and a genotypically indistinguishable strain of L. longbeachae was cultured from this material. Following examination of a national collection of Legionella isolates, two more patients with indistinguishable genotypes were identified. One of these patients had visited a garden centre in the same municipality in which the index patient had acquired his potting soil. The study demonstrated the value of systematic collection of identification data and patient isolates over a prolonged period.