AIM: To evaluate the incidence of portal hypertension (PHT) in biliary atresia (BA) patients and to monitor its progress after Kasai portoenterostomy (KP) by measuring nitric oxide (NO) levels in peripheral blood.MATERIALS AND METHODS: A prospective cross-sectional study conducted over a period of 2 years. Intraoperative portal pressure (PP) and blood NO levels at presentation, 1-month, 3-month, and 6-month follow-up, were correlated with clinical and biochemical parameters in BA patients. The mean NO level in age-matched control group was 4.64 ± 2.32 mumol/L.RESULTS: Thirty-four BA patients underwent KP over a period of 2 years. The mean age of presentation was 2.7 months (range 1-4 months). The mean intraoperative PP was 21.3 ± 5.4 mmHg. The mean PP in patients aged <60 days, 61-90 days, and >90 days was 18.53 ± 4.45 mmHg, 20.33 ± 3.07 mmHg, and 26.5 ± 5.01 mmHg, respectively. The mean PP in the patients who underwent successful KP was 16.75 ± 3.54 mmHg while for those who continued to have jaundice it was 23.94 ± 4.63 mmHg (P < 0.001). NO levels closely followed the PP as shown by the regression equation NO = 4.79 + 0.64 PP mmHg, R (2) = 0.69. The mean NO level at presentation was 18.48 ± 4.17 mumol/L and at 1-month, 3-month, and 6-month follow-up was 11.94 ± 5.62 mumol/L, 10.79 ± 6.02 mumol/L, and 9.93 ± 6.53 mumol/L, respectively (P < 0.001). The difference in NO levels was also statistically significant between the patients who cleared jaundice and those with persisting jaundice.CONCLUSION: All BA patients had PHT at presentation. PHT worsens with age and has an adverse effect on outcome of KP. NO levels in blood closely follow PP and higher levels are associated with poor outcome.