Introduction Premature labor is a serious worldwide problem that can cause neonatal death and other serious disorders. This study aimed to determine the most important factors related to preterm labor in Yasuj, Iran. Method This case-control study was conducted in the maternity ward of Imam Sajjad Hospital, the obstetrics and gynecology center of Yasuj, in 2010. Among eligible samples, mothers with preterm labor were selected as the case group, and for each sample in the case group, one mother with full-term labor was selected by using clipper-matched sampling to make up the control group. Data were collected by a researcher-made questionnaire and the 28-item General Health Questionnaire. Finally, after deleting imperfect questionnaires, collected data of 52 subjects of case group and the same amount in control group were analyzed. Results Among the 5400 live birth infants in Yasuj in 2010, 130 infants were premature (2.4%). The preterm labor risk in women with two or more pregnancies was 5.5 times more than women with less than two pregnancies, its risk in women with low general health status was 2.9 times more than in women with normal general health status, and the preterm labor risk in women with a history of diabetes mellitus/thyroid dysfunction/cardiac disease was 2.3 times more than healthy mothers (P < 0.01). Conclusion With respect to the above and due to the role and importance of mother–infant health in community health, it is necessary that the health-care system improve health education with regard to the appropriate number of pregnancies, diagnose and cure disease during pregnancy, especially diabetes and cardiovascular disease (hypertension and/or eclampsia), and recognize pregnant mothers with mental pressure or lack of sufficient support and help them.