['The aim of this study was to assess the prevalence of elevated transaminase levels in children undergoing prophylactic treatment for tuberculosis (TB) infection.', 'All children living in a geographically defined area, who started TB prophylaxis during 2009-2011, were included. Data on background factors, treatment regimes and transaminase levels at baseline and follow-up were collected retrospectively.', 'Of the 277 children who were treated, 113 (41%) had elevated transaminase levels. Of these, 97 (35%) had levels that were less than three times the upper limit of the normal range and 16 (6%) had levels that were more than three times the normal range. Four patients had to discontinue isoniazid treatment and were successfully switched to rifampicin. In 17 patients, the highest transaminase peak did not occur until after 6\xa0months of treatment. Elevated transaminases were significantly more common in patients below 9\xa0years of age (62%) than in those aged 10-18\xa0years (28%). Transaminases were elevated in 44% of all boys and 36% of all girls (p\xa0=\xa00.17).'] Are elevated transaminases common in children on prophylactic treatment for tuberculosis?