A war photographer, documentary-maker and portraitist, Nilsson used an ultra-fine tube called an endoscope, to take pictures of cells and blood vessels, and went on to take images of human foetuses and embryos.
His 1965 book, “A Child is Born,” was one of the most successful photography albums ever, selling in the millions and becoming an iconic work for the anti-abortion movement.
Only later did it become widely known that many of the embryos used in the photo-essay were not alive, as many readers had thought, but had been aborted.
At Sweden's Karolinska Institutet, Nilsson went on to explore scientific photography.
He is commonly credited with the first photographs of the AIDS virus and the Severe Acute Respiratory Syndrome (SARS) virus, using a scanning electron microscope.
Below is a photo of Lennart Nilsson attending a 2015 exhibition of his work. (Maja Suslin/TT)