To compare the difference between primary proximal renal tubular acidosis (PRTA) and Fanconi syndrome (FS), and to find out possible risk factors for growth retardation, we studied the long-term growth, clinical, laboratory, and radiological findings associated with the treatment of six children with primary FS and 15 children with PRTA. The ages of the children with FS were much older than those with PRTA at initial diagnosis (7.03±3.82 vs. 1.63±1.56 years). The height standard deviation score ( SDS) at the start of treatment was significantly lower in FS than in PRTA. Catch- up growth was noted in PRTA at the end of follow-up ( initial height SDS –2.13±1.10 vs. last height SDS –1.33±1.43, P=0.023 by paired t-test), whereas apparent linear growth impairment was found in FS in terms of overall growth velocity index (82.70±8.37%) and height SDS ( initial –3. 25±0.95 vs. last –3.15±0.31, P=0.791). There was also a higher rate of rickets occurrence in FS (3/6 vs. 0/15 in PRTA). Hypophosphatemia during the follow-up period was more frequent for FS than PRTA (69.2±26.1% vs. 7.0±25.8%, P