Undernutrition is an inadequate supply of energy and nutrients. Periodontal diseases (PDs) are defined as a broad form of chronic inflammatory disease of the gingiva, bone and ligaments supporting the teeth. This study aimed to reveal the relationship between undernutrition, using body mass index (BMI) and serum albumin level (Alb), and PDs in a sample of Yemeni population. A cross-sectional study was conducted at dental teaching clinics at the Faculty of Dentistry, Sana’a University. Of the 1920 patients attended to clinics, only 229 matched the study criteria. Oral examination was performed to assess the periodontal clinical parameters measurements. BMI and Alb was measured. Participants of both genders were involved with slight increase in males (n = 134, 58.5%) and most of the study sample was at the age group of (18–35) (n = 209, 91.3%). Regarding to habits, only (n = 43, 18.2%) of patients were smokers and about half of participants (n = 136, 59.4%) were khat chewers. Most of cases had a mild undernutrition according to BMI (n = 139, 60.7%) and normal Alb level (n = 213, 93%). Regarding the periodontal diagnosis, most of the participants were diagnosed with gingivitis (n = 186, 81.2%). BMI and albumin level were non significantly associated with PDs. PDs were statistically significant with the participant’s age, gender, level of education and smoking (P ≤ 0.05). Whereas, BMI, khat chewing, and Albumin level were non-significant factors of periodontal diseases among Yemeni participants (P > 0.05). In both genders, variables such as age of the patients, smoking, khat chewing and PDs were non-significantly associated with BMI. This study showed that the majority of the participants had diagnosed with gingivitis but there was not an association between PDs and undernutrition This paper is presented on research square URL:// https://www.researchsquare.com/article/rs-429796/v1 with DOI: 10.21203/rs.3.rs-429796/v1