Ismā‘īl ibn Ḥasan Jurjānī (circa 1042–circa 1136, also seen as Jorjānī and Gurjānī), known popularly as Hakim Jurjānī, was among the most famous physicians of 12th-century Iran. In the period between the Islamic conquest and the time of Jurjānī, almost all scientific books by Iranians were written in Arabic, including such famous works as al-Qānūn fī al-tibb (The canon of medicine) by Ibn Sina (Avicenna). Jurjānī's medical encyclopedia, Zakhīrah-i Khvārazm’Shāhī (The treasure of Khvarazm’Shah) was the first major medical book in post-Islamic Iran written in Persian, and it soon became a primary resource for Iranian physicians, used for many centuries. It also was translated into Hebrew, Urdu, and Turkish. The voluminous work is in ten parts. In a lengthy preface, Jurjānī describes in detail the climate, geography, and the common diseases of Khvarasm (present-day Khorasan), the northern province where he lives. After presenting this background, he explains the necessity of writing a medical textbook in his native language. The arrangement of the ten parts of Zakhīrah is similar to Avicenna’s Canon. In current medical terminology, the ten parts discuss the following topics: (1) anatomy, physiology and knowing temperaments, humors, and elements; (2) general pathophysiology (including a chapter describing the kinds of pulses and a chapter on causes of death); (3) hygiene and nutrition (including separate chapters on diseases of childhood, of age, and especially diseases contracted while traveling); (4) diagnoses and prognoses; (5) fever and its classification; (6) treatments (the volume of the encyclopedia most sought after by physicians of the period); (7) infectious diseases; (8) skin diseases; (9) toxicology; and (10) pharmacology. The present manuscript, created in the 12th century, has remarkable illustrations and illuminations and is one of the oldest existing copies of Zakhīrah. It is preserved in the manuscript collections of the National Library and Archives of the Islamic Republic of Iran.