Vanillylmandelic acid (VMA) is one of the metabolites of catecholamines including epinephrine and norepinephrine that was excreted into the urine. Analysis of urinary concentrations of VMA was useful to the diagnose of pheochromocytoma and neuroblastoma. Generally, the measurement of VMA use urine 24-hour urine collections, but in pediatric patient, it was difficult to collection the urine sample. Therefore, the random urine was accepted because it was found that the VMA concentration in random and 24-hour urine had no statistically significant difference. VMA will decompose at alkaline conditions, therefore, to preserve the VMA concentrations, the urine should be acidified or kept frozen. The aim of the study was to compare the VMA levels in frozen and acidified random urine. We performed the study by collecting of 33 urine samples at the Clinical Chemistry Unit, Songklanagarind Hospital. The urine was aliquot 5 ml into 2 containers, one kept frozen at -20 ๐C, and the other was acidified with 6N HCL 200 μl and stored at 4 ๐C. Then, the urinary VMA concentration was determined by modified method of Gumboldt. The results showed that the X±S.D. of VMA concentration in frozen and acidified random urine were 23.43 (45.38) and 24.57 (54.45) μg/mg creatinine, respectively. The VMA concentration in frozen and acidified random urine was correlated well (r=0.997) and showed no statistically significant difference (p=0.713)