This cross-sectional analytic study aimed to investigate any relationship between the body mass index (BMI) and an abnormal Pap smear. The subjects were 7,720 women aged 30-69 years who lived in Khon Kaen Province, Thailand, and had been recruited as participants in the Khon Kaen Cohort Study during 1990-2001. All had received Pap smear screening for cervical cancer. The data were analyzed using descriptive and inferential statistics. Multiple logistic regression was used to determine the relationship between body mass index and an abnormal Pap smear. The mean BMI was $24.53kg/m^2$ (SD=3.98), and 2.14% had abnormal Pap smears. Compared with the reference group of women with a BMI ${leq}22.9kg/m^2$, those with a body mass index of $23.0-24.9kg/m^2$ had a reduced risk of an abnormal smear (ORadj=0.92, 95%CI: 0.57-1.47), but women with a BMI $25.0-29.9kg/m^2$ were found to have an approximately 1.24 times higher risk ($OR_{adj}=1.24$, 95%CI: 0.86-1.80), and those with a BMI ${geq}30.0kg/m^2$ had an approximately 1.63 times higher risk ($OR_{adj}=1.63$, 95%CI: 0.98-2.69). The results indicated that the risk of Pap smear abnormalities is increased in women who have a higher than normal body mass index, but this finding was not statistically significant. Nevertheless, public health personnel should encourage women to maintain their BMI in the normal range to reduce the possible future risk of cervical cancer.