BackgroundEarly Childhood Caries (ECC) is a highly prevalent disease among preschoolers in Sri Lanka, with stagnated prevalence over the decades. Therefore, it is important to determine the socio-behavioural associations of ECC among preschoolers to reduce the country’s ECC burden.MethodsA cross-sectional study with a multistage cluster sampling technique was used to select 3 to 4 year-old preschoolers/mothers dyads in Gampaha district in 2019. Preschoolers who completed third birthday and had not completed fifth birthday on the day of data collection were selected. The dependent variable was the presence (dmft ≥ 1) or absence (dmft = 0) of ECC. Independent variables were sex, monthly family income, mother’s educational and occupational status, child’s birth order, family type, frequency of consumption of sweets and sweetened drinks, time of sweet consumption during the last 24 h, toothbrushing frequency, supervision of toothbrushing, dental visit, and maternal dental caries. A pre-tested validated questionnaire was used. Multiple logistic regression analysis was used.ResultsTotal of 1038 preschoolers were selected. There were 529 females (51.0%) and 509 males (49.0%). The prevalence of ECC was 56.3% (95% CI: 53.1–59.3). Consuming sweets between meals had a higher odds ratio than consuming sweets after main meals (OR = 1.72, 95% CI:1.25–2.35), consumption of sweets every day had a higher odds ratio than consumption of sweets several times a week or less (OR = 2.89, 95% CI: 2.02–4.13), consumption of sweetened drinks every day had a higher odds ratio than consumption of sweetened drinks several times a week or less (OR = 1.73, 95% CI: 1.07–2.79), and the presence of maternal caries had a higher odds ratio than the absence of maternal caries (OR = 1.74, 95% CI: 1.12–2.69). The use of adult fluoridated toothpaste than not using adult fluoridated toothpaste (OR = 0.64, 95% CI:0.48–0.85), tooth brushing twice per day than not brushing twice per day (OR = 0.67, 95% CI:0.51–0.89), and supervised toothbrushing than unsupervised toothbrushing (OR = 0.61, 95% CI: 0.41–0.93) was negatively associated with ECC.ConclusionsECC is highly associated with sweet consumption and oral hygiene behaviours among preschoolers in Gampaha District. Interventions should focus on the oral health behaviours of preschoolers to reduce ECC burden.