Background: Gingival enlargement is usually noted within one to two months after the initiation of nifedipine therapy. The aetiology of nifedipine-induced gingival overgrowth is uncertain. The aim of this study was to determine the relationship between plasma and gingival crevice fluid (GCF) nifedipine concentrations and the degree of gingival overgrowth in patients treated with nifedipine, and also to assess the correlations between clinical and pharmacological variables. Methods: Eighteen patients taking nifedipine in regular doses for at least six months participated in the study. Gingival enlargement was evaluated with two indices to score vertical and horizontal overgrowth. Gingival index (GI), plaque index (PI), gingival bleeding time index (GBTI), probing depth (PD) and clinical attachment level (CAL) were also evaluated. GCF and plasma nifedipine concentrations were determined by using high performance liquid chromatography. Results: There was no significant difference between responders and non-responders for PI, GI and GBTI. The mean concentration of nifedipine in GCF was significantly greater than concentration in plasma. No significant difference was observed for GCF and plasma nifedipine concentration between responders and non-responders. Conclusions: The present study showed that neither GCF nor plasma nifedipine levels appeared to be a risk factor for nifedipine-induced gingival overgrowth. Improving the oral hygiene in patients using nifedipine may help control the degree of drug-induced gingival enlargement.