In order to understand the role of the factors that can predict the comprehension of health-related texts in a second language (L2), we conducted a study that examines whether allowing L2 users to listen to a health-related text while reading it affects understanding. We also investigated what role general and health-related vocabulary knowledge play in the comprehension of health-related texts in a silent-reading and reading-while-listening conditions. Our participants were 259 Sri Lankan L2 users who read two health-related texts silently and read two other texts while listening to the text being read out to them. They also completed an L2 vocabulary knowledge and a health-related vocabulary knowledge test. We used Generalized Linear Mixed-Effects Models to predict the effect of text presentation mode, L2 and health-related vocabulary knowledge on comprehension. The results showed no significant effect of text presentation mode. However, both L2 vocabulary knowledge and health-related vocabulary knowledge were found to play a substantial role in text comprehension. Our findings also revealed that Sri Lankan L2 users generally demonstrated inadequate comprehension of health-related texts. To promote a higher level of health-related text comprehension in an additional language, the general and health-specific L2 vocabulary knowledge and language proficiency of the population needs to be improved.