To assess lung perfusion patterns in inpatients with acute viral bronchiolitis using quantitative 99mTc-MAA scintigraphy so as to establish an association with clinical and radiological findings.A comparative, prospective case series study with a focus on diagnosis was carried out in a population of patients with acute viral bronchiolitis admitted to Hospital de Clínicas de Porto Alegre. Inclusion criteria were age between 1 and 24 months and first sudden-onset wheezing episode, suggesting bronchiolitis. The patients in the study were submitted to clinical, radiological and 99mTc-MAA lung perfusion evaluation during the first 24 hours of admission. Statistical analysis employed t test, taking into consideration a significance level of 0.05.The regional distribution of lung blood flow in the 38 patients studied was more pronounced in the upper section of the left lung in relation to the right lung (P1.0 in the upper and middle sections of both lungs. In the lower section it was >1.0 only in the right lung (P<0.007). There was no association between lung blood flow distribution patterns and clinical or radiological findings.There was no evidence of an association between lung blood flow distribution and ventilation-perfusion ratio in hospitalized infants with acute viral bronchiolitis; only a tendency to redirect lung blood flow towards upper lung sections was observed.