Objective To investigate the incidence of urolithiasis in infants aged 0-3 years old fed by melaminetainted milk powder in Gansu province. Methods Questionnaires were distributed to 7 856 infants who were screened for urolithiasis in the Second Hospital of Lanzhou University by ultrasound examination from September 25, 2008 to November 15, 2008. Data were collected by Excel and analyzed by SPSS 13.0 software. Results A total of 4 090 (52.06%) male infants and 3 766 (47.94%) female infants underwent ultrasound examination in the Second Hospital of Lanzhou University. The mean age of the infants with urolithias was 18.30±9.68 months. Of those, 704, including 434 males (61.65%) and 270 females (38.35%), were diagnosed with urolithiasis, with an incidence of 8.96%, and 99.14% of calculus was located in kidney. And, 58 aged 0-6 months with an incidence of 3.16%, 218 aged 6-12 months with an incidence of 11.01%, 275 aged 12-24 months with an incidence of 12.55%, and 153 aged 24-36 months with an incidence of 8.27%. The relationship between the incidence of urolithiasis and gender as well as age was assessed by using the Pearson Chi-square test. The results showed significant differences in the incidence of urolithiasis among infants of different genders and different ages (Plt;0.05). The result of multiplelogistic regression analysis indicated that gender was related to the incidence of urolithiasis (Plt;0.05). Conclusion The incidence of urolithiasis in the infants aged 0-3 years old in Gansu province is relatively high. The incidence of urolithiasis focuses on the infants aged 6-24 months and has anatomical specificity.