Eleven previously unpublished letters written by N.I. Pirogov to A.L. Obermiller in 1877‒1880 have been discovered. Three of them were published in 2013 for the first time. Presented unabridged for the first time are two letters relating to the start of this correspondence, which contain Pirogov’s treatment recommendations for the illness afflicting the chief of the Danube army, Grand Duke N.N. Romanov (senior), whose court physician was Obermiller. Pirogov participated in the treatment of the Grand Duke from December 1876 to January 1877 in Chisinau, where the headquarters of the commanderin-chief was located. Once the risk of complications in the patient had passed, Pirogov returned to the estate of Vishnya, from where he continued medical consultations for the Grand Duke via correspondence with Obermiller.