Relatively little data exist concerning the manifestations of repeated obstructive sleep apnea in normal infants. A questionnaire concerning daytime and sleep habits was completed by the parents of 4,100 healthy infants before they underwent a 9-hour night monitoring study. One hundred infants with an obstructive apnea index above 1.2 were randomly selected. They formed the "apnea" group. From the initial population, 300 infants with no apnea were also selected to form the "no-apnea" group. Both groups were matched for sex, gestational age, post conceptional age, birth weight, mother's age, parity and a family history of sudden infant death. Five variables from the questionnaires significantly differentiated the two groups of infants. When awake, the infants with apnea were characterized by a greater frequency of breathholding spells (22% of apnea infants) and episodes of fatigue during feeding (28%) than the non-apnea infants. During sleep, they exhibited a greater frequency of profuse sweating (15%), snoring (26%) or noisy breathing (44%). Multiple symptoms were present in some infants. A stepwise logistic regression resulted in two significant independent variables: profuse sweating during sleep (p = 0.008) and noisy breathing (p = 0.002). The predictive value of these two symptoms was tested on a new group of 650 healthy infants. The two independent variables led to the correct classification of 60 of the 67 infants with apnea (89.67%) and 382 of the 583 non-apnea infants (65.5%). A positive history alone had a positive predictive value of 0.21.(ABSTRACT TRUNCATED AT 250 WORDS)