This retrospective study summarises the results of the analyses of 4495 canine and feline uroliths submitted to Minnesota Urolith Center, USA, from Benelux veterinarians between 1994 and 2004. The composition of uroliths changed during this period. Feline struvite uroliths became less prevalent (from 77% to 32%) whereas calcium oxalate uroliths became more prevalent (from 12% to 61%). The same trend was observed in dogs (51% to 40% and 33% to 46% respectively).