Cotinine is the main metabolite of nicotine and is used as an indicator of exposure to tobacco smoke. A method has been developed for quantification of cotinine in pericardial fluid and whole blood collected from autopsy casework involving cases of infant death. Sample clean-up was achieved by solid-phase extraction with a mixed-mode column. Cotinine was quantified by liquid chromatography-tandem mass spectrometry. Positive ionization was performed in the multiple reaction monitoring mode. Two transitions were monitored for the analyte and one for the internal standard, cotinine-d(3). The calibration range was 0.9-176 ng/mL for cotinine in both matrixes. The recovery of the analyte ranged from 86 to 92%, and the between-assay precisions ranged from 4 to 6% relative standard deviation. Whole blood and pericardial fluid samples from 95 infant deaths obtained during autopsy were analyzed. A strong correlation (R(2) = 0.97) was found between the cotinine concentrations in pericardial fluid and blood. The correlation was not affected by the postmortem time interval. This study demonstrates that pericardial fluid may be an alternative specimen to blood for quantification of cotinine in forensic autopsies.