Aim: To investigate the efficacy and safety of home-treatment with oral piv-mecillinam or amoxicillin-clavulanate in children with acute pyelonephritis. Methods: Children aged over 6 months diagnosed with culture confirmed pyelonephritis at Danish Paediatric Departments were home-treated with piv-mecillinam (tablets) or amoxicillin-clavulanate (liquid or tablets). Follow-up was performed by phone (second treatment day) and clinical review of the patients in the hospital (day three). Results: Four hundred eighteen children were included. In total, 333/418 (80%) responded well to the initial oral antibiotic treatment. 85/418 (20%) were changed to another treatment of these 47/418 (11%) to a second-line oral antibiotic and 38/418 (9%) to intravenous antibiotics due to insufficient clinical improvement or bacterial resistance. Bacterial resistance was similar for piv-mecillinam and amoxicillin-clavulanate: 4/74 (5%) versus 33/333 (10%) (p = 0.22). Insufficient clinical improvement, despite no resistance, primarily occurred in children treated with piv-mecillinam: 16/74 (22%) versus 28/344 (8%) (p < 0.001), and predominantly occurred in piv-mecillinam treated children <5 years: 7/20 (35%) versus 9/54 (17%) (p < 0.05), potentially because of problems with piv-mecillinam tablets. In the study population no cases of death or septicemia developed after start of initial oral treatment. Conclusion: A home-treatment regime for pyelonephritis in children >6 months is safe; however, during treatment, clinical re-evaluation is required as in 20% of cases a change in treatment was necessary.