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Background Fraction of exhaled nitric oxide (Feno) level is used as an aid in the diagnosis and management of chronic asthma. Its role in acute asthma remains to be studied. Objective To determine whether Feno levels are elevated in children with asthma exacerbations compared with baseline, and whether there is a difference in Feno levels based on PCR positive (+) (respiratory virus isolated by PCR analysis) versus PCR negative (−) (respiratory virus not isolated by PCR analysis) status. Methods Children with a previous Feno level measurement while stable and who presented to an urgent care facility with an asthma exacerbation were enrolled. Feno levels, spirometry, and nasal swabs for viral PCR were obtained at the time of the exacerbation and following a course of prednisone. Data were available on 66 children. Linear mixed models were used to regress the outcomes of interest (FEV1, FEV1/forced vital capacity, forced expiratory flow at 25% to 75% of forced vital capacity, and natural log Feno) on detected virus (yes/no), visit (baseline, exacerbation, follow-up), and the interaction between the detected virus and visit. Results Compared with baseline, higher Feno values and lower lung function were found at the time of an exacerbation. A respiratory virus was detected in 59% of the exacerbations. The interaction between PCR (+) and PCR (−) groups and visit on log Feno was marginally significant (P = .07). There was no difference in log Feno between the PCR (+) and PCR (−) groups at baseline, while higher log Feno was found in the PCR (−) group at the time of exacerbation and following prednisone (P = .05 and .001, respectively). Conclusions Higher Feno concentration in PCR (−) exacerbations suggests an eosinophilic predominance in nonviral compared with viral exacerbations.