From 1994 to 2004, Hill's Pet Nutrition received 4495 canine (65%) and feline (35%) uroliths from Benelux veterinary practitioners. They were sent to the Minnesota Urolith Center, USA for analysis. In 1994, 110 uroliths were analysed - 85% from dogs - and in 2003, 1067 uroliths were analysed - 59% from dogs. During this period, substantial changes were observed in composition. In 1994, 77% of the cats had uroliths composed of struvite, and 12% had uroliths composed of calcium oxalate. In 2003, feline uroliths were composed of 32% struvite, and 61% calcium oxalate. The same evolution was observed in the dogs. In 1994, 51% of canine uroliths were composed of struvite, and 33% of calcium oxalate. In 2003, 40% had struvite uroliths, and 46% had calcium oxalate uroliths. A significant effect of the size, the breed, and the gender were noticed in the dogs. The mean age of uroliths appearance was 7.3 years in the dogs and 7.2 years in the cats. The findings are similar to those previously published in the USA.