Tritrichomonas foetus (T. foetus) is a flagellated protozoan parasite that has been identified as a natural and experimental cause of large bowel diarrhoea in domestic cats.3 The diagnosis of T. foetus depends on the demonstration of live organisms by direct microscopic examination of fresh faeces, faecal culture or extraction of DNA in faeces by polymerase chain reaction (PCR).1,2 The global prevalence of T. foetus infection in domestic cats, with and without diarrhoea, ranges from 0-81.8%.2 The aim of this study was to assess the overall and regional prevalence of T. foetusfeline faecal samples in Spain using RT-PCR. The study was performed retrospectively, including faecal samples submitted to a reference laboratory during a 10-year period (2010 to 2020). Faecal samples of 2062 cats were assessed for the presence of T. foetus DNA using RT-PCR methodology. In the present study, the overall prevalence of infection was 13.3%. T. foetus infected cats were younger than negative cats. Follow-up analysis was available for 101 cats (3.8%). In 45 (44.5%) had a negative result for all tests, 37 cats (36.6%) tested positive initially with a negative subsequent test, and 17 cats (16.8%) were positive on all tests. Two cats (1.9%), were negative initially and positive on subsequent testing. To the author\'s knowledge, this is the first prevalence study of T. foetus that include different areas of Spain. The current study indicates that T. foetus infection may be found frequently in cats in Spain, suggesting that it may be a common cause of diarrhoea in cats in this country.