Patient perception of uterine activity was assessed objectively in 44 women at risk for preterm labor using a tocodynamometer designed for ambulatory outpatient use. The monitor allowed patient-activated marking of the data whenever contractions were perceived. After instruction in self-detection of uterine activity, tocodynamometry was performed daily for 8.5 weeks per patient. Patients identified an average of 15% of their contractions during the study (range 0–78%). Numerous marks were placed in the absence of any detectable uterine activity. Of multiple obstetric variables analyzed, only multifetal gestation and preterm labor in the current pregnancy had any significant impact on perception. Results suggest that self-detection of uterine activity may not be reliable as the only means for the earliest possible detection of preterm labor.