This is the first talk, but not the last, given by Dorothy Crowfoot Hodgkin at the Lindau meetings. Six years after her Nobel Prize in Chemistry, she is still occupied with the crystal structure of insulin, a project she started in Oxford in 1934, more than 35 years earlier! She had then just spent two years with J.D. Bernal in Cambridge, learning the basics of crystallography of biological molecules. The choice of the special protein insulin was made because it plays such an important role in the body. In the story Hodgkin tells here, there are also many remarks as to the appearance and function of insulin in the body. But mostly, the story unravels some of the difficult technical steps involved in understanding the crystal structure of insulin. Since the lecture was given with many slides, this is not the right place to learn all the details, but the general story clearly comes through. One question treated is the molecular weight of the insulin molecule. Chemistry Nobel laureate The Svedberg had used his invention the ultracentrifuge and answered 36 000 units, but it turned out that he had measured particles of insulin, not molecules. Frederick Sanger, another chemist who also received the chemistry Nobel Prize, managed to determine the chemical structure of insulin by cracking it into its pieces. (He told his story at Lindau in 1960.) Insulin turned out to have molecular weight around 6 000 units, much smaller than Svedberg believed, but still big enough to give rise to many difficulties. One such was the need to insert heavy atoms in the crystals, a general method employed to get more information out of the thousands of X-ray diffraction pictures taken and inspected. At the National Portrait Gallery in London there is a wonderful painting of Dorothy Crowfoot Hodgkin working with her tables of crystallographic data using no less than four (!) hands.