To study the origin of the idea that herpes labialis in patients with pneumonia and meningitis was believed to have a prognostic signification.

A selection of 19^th and 20^th century textbooks and referred articles was consulted. The following characteristics were studied: association between meningitis and herpes, type of meningitis, diagnostic significance, and prognostic significance. In addition the HL-pneumonia association was studied.

The Strasbourg physician Charles-Polydore Forget was the first to describe the HL-meningitis association in 1843. Tourdes (1843), Drasche (1859), and Salomon (1864) attributed a favorable prognostic significance to the HL-meningitis association. In a comprehensive monograph (1866), August Hirsch, although confirming the association, denied the prognostic significance through critical analysis of the data. A few authors attributed a diagnostic significance to the occurrence of HL, suggesting meningococcal meningitis.

The HL-meningitis association, but not the prognostic significance, has been mentioned in most neurological textbooks since then. In contrast to meningitis, in which a prognostic attribution of HL was only a short-lived 19^th century idea, the favorable prognostic significance of HL in pneumonia continued to be described up to the 1950s. A possible protective effect of herpes viruses has been published in recent years. One wonders whether the disappearance of the prognostic HL-pneumonia significance, could be associated with the introduction of antibiotics in the late 1940s.