The second half of the 19th century witnessed an increasing interest in neurology and psychiatry by Portuguese physicians, in parallel with the overall development of these disciplines in other countries. This process is reflected in the numerous case report publications as well as in debates taking place at the Lisbon Society of Medical Sciences, the major scientific forum of that time. The 'Ajuda Paralyses' were a mysterious succession of epidemics that occurred during 1860-64 in the Ajuda asylum for cholera and yellow fever orphans, which were extensively discussed during 1865-66 by Bernardino Antonio Gomes, Antonio Maria Barbosa, Abel Jordão and Eduardo Motta. Studying this debate helps understand the initial stages of development and the great interest that 'nervous diseases' had for Portuguese clinicians in the mid-19th century and possibly provides one of the first modern descriptions of nutrition-related polyradiculoneuropathy and the ocular findings associated with avitaminosis A. This debate took place at a decisive time for the scientific development of neurology and psychiatry, concurrent with the widespread application of the clinical-anatomical method and neuropathology to the study of diseases of the nervous system, which would set the foundations for our own modern pathophysiological framework. Therefore, the 'Ajuda paralyses' debate also provides a good basis for a discussion on the evolution of the concepts of hysteria and psychosomatic disease and the description of peripheral neuropathy from among a wealth of other entities that did not withstand the test of science.