Objectives: Medical education requires student comprehension of both technical (scientific/medical) and non-technical (general) vocabulary. Our experience with "English as a second language" (ESL) Arab students suggested they often have problems comprehending scientific statements because of weaknesses in their understanding of non-scientific vocabulary. This study aimed to determine whether ESL students have difficulties with general vocabulary that could hinder their understanding of scientific/medical texts. Methods: A survey containing English text was given to ESL students in the premedical years of an English-medium medical school in an Arabic country. The survey consisted of sample questions from the Medical College Admission Test (USA). Students were instructed to identify all unknown words in the text. Results: ESL students commenced premedical studies with substantial deficiencies in English vocabulary. Students from English-medium secondary schools had a selective deficiency in scientific/medical terminology which disappeared with time. Students from Arabic-medium secondary schools had equal difficulty with general and scientific/medical vocabulary. Deficiencies in both areas diminished with time but remained even after three years of English-medium higher education. Conclusion: Typically, when teaching technical subjects to ESL students, attention is focused on subject-unique vocabulary and associated modifiers. This study highlights that ESL students also face difficulties with the general vocabulary used to construct statements employing technical words. Such students would benefit from increases in general vocabulary knowledge.