A fast and reliable method was developed for the determination of fluoride in toothpaste based on the headspace single drop microextraction (HS-SDME) followed by gas chromatography/flame ionization detection (GC/FID). The method is based on the volatilization of fluoride using trimethylchlorosilane as the derivatization reagent to form trimethylfluorosilane at acidic pH. The trimethylfluorosilane formed is preconcentrated in a 0.8 μL drop of mesitylene suspended from the tip of a common GC microsyringe to the headspace of the sample. Parameters such as nature of the extraction solvent, extraction time, size of the microdrop, sample volume, stirring rate, derivatization reaction time and pH of the sample solution were studied and optimized. The developed protocol was found to yield a linear calibration curve in the concentration range of 5.0–39.0 mg L−1 with a limit of detection of 4.4 μg L−1 with a good enrichment factor of 58.8 for the analyte. The repeatability of the method was satisfactory (RSD ≤ 5.41%). The total analysis time including microextraction and gas chromatography analysis was less than 30 min. Because preconcentration and sampling are performed from the headspace of the sample, this method is suitable for the determination of trace amounts of fluoride in toothpastes and water samples.