AIM: Recent data have shown that superior mesenteric artery (SMA) flow rates are significantly increased in active Crohn's disease, suggesting that SMA flow may be a useful, non-invasive index of disease activity. The aim of this prospective study was to evaluate the use of SMA Doppler sonography as an indicator of Crohn's disease activity and to compare with clinical evaluation and the Crohn's disease activity index (CDAI). MATERIALS AND METHODS: Patients with active Crohn's (n = 19), inactive Crohn's (n = 17) and control subjects (n = 17) were evaluated. Categorization of disease activity was based on a reference standard. CDAI scores were also calculated independently. The SMA flow parameters evaluated were resistive index, pulsatility index, end diastolic velocity, peak systolic velocity, time averaged maximum velocity, cross-sectional area and maximum flow volume. RESULTS: Using a three-group ANOVA for each of peak systolic velocity (PSV) (P = 0.01), end-diastolic velocity (EDV) (P = 0.04), pulsatility index (PI) (P = 0.003), time-averaged maximum velocity (TAMV) (P = 0.05), and maximum flow volume (TAMV.CSA) (P = 0.01), there was a significant effect of group. Using post-hoc tests, only EDV (P = 0.01), TAMV (P = 0.02) and TAMV.CSA (P = 0.003) were significantly different between active and inactive Crohn's disease, though with considerable overlap of values for EDV and TAMV. The mean CDAI scores were significantly different between patients with active Crohn's (287) and inactive Crohn's (71) (P = 0.0001) and correlated well with the reference standard. CONCLUSION: Only three of several parameters previously described as allowing Crohn's disease activity assessment actually did so in our study. However, for two of these parameters (EDV, TAMV), there was overlap between the measurements in the active and inactive groups, thus limiting the ability to discriminate disease activity in practice. The degree of overlap for maximum flow volume (TAMV.CSA) between active and inactive disease was considerably less and this parameter may be more discriminatory of disease activity. On the other hand, we found CDAI scores to be accurate in disease categorization. We agree that there appear to be hyperdynamic changes in active Crohn's disease but suggest that Doppler ultrasound assessment does not reliably assess disease activity in routine clinical practice.