Antimicrobial peptides play an important role in the local defence of oral cavity. Cigarette smoke has detrimental effects on immune defence mechanisms. The effect of passive smoking on salivary LL-37, as an antimicrobial peptide, in children has not yet been reported.The aims of this study were to evaluate salivary LL-37 levels in PS-exposed and PS-unexposed children and to investigate the association between salivary LL-37 levels and periodontal clinical parameters.Unstimulated salivary samples were collected from 180 children (90 PS-exposed [38 girls and 52 boys; mean age: 9.36 ± 1.60 years] and 90 PS-unexposed [43 girls and 47 boys; mean age: 9.02 ± 1.71 years]) in this study. Periodontal clinical parameters, including plaque index (PI), gingival index (GI), probing depth (PD), and clinical attachment level (CAL), were recorded in all children. Salivary cotinine and LL-37 levels were measured by enzyme-linked immunosorbent assay.PI and GI values in PS-exposed children were significantly higher than those in PS-unexposed children. The mean salivary cotinine concentration was significantly higher in PS-exposed children than in control subjects. The mean salivary LL-37 concentration of PS-exposed children was significantly lower (100.71 ± 72.14 pg/mL) than that of PS-unexposed children (151.84 ± 107.89 pg/mL).Passive smoking could suppress salivary LL-37 concentrations in children.