He was interested in rare diseases affecting the gut throughout his life, and one such, atresia of the oesophagus and small bowel, was the subject of his doctoral thesis, presented in May 1861.

[6] He was not a great teacher, however, having problems with public speaking and a penchant for focusing on rare cases rather than those most beneficial to general practice.

[7] Hirschsprung offered free health care for poor children while continuing to require patients with more means to pay.

He continued his study of what would later come to be called Hirschsprung's disease until his poor health prevented him, and lived out his retirement in his country house in Øresund.

[9] Hirschsprung published on many areas of pediatrics, including pyloric stenosis, intussusception, rickets, and rheumatic nodules, but he is most well known for his work on the disease that later came to bear his name.