Prior studies have found an increased incidence of adverse perinatal outcomes of pregnancies in asthmatic mothers, however, these studies are limited by lacking of categorization of asthma severity. This study prospectively examined the relationship between severity of asthma during pregnancy and infant and maternal outcomes. A total of 82 pregnant asthmatic women (32 with mild asthma, 26 with moderate asthma and 24 with severe asthma) and 95 pregnant non-asthmatic control women were finally included in the study. All women were subjected to thorough history taking, complete clinical examination, routine investigations, abdominal sonography, pulmo- nary function tests and Doppler ultrasound of the umbilical artery. The asthmatic and control groups were well matched with regard to age, weight, height, smoking, gravidity and parity. The forced expiratory volume in one second was significantly reduced in women with severe asthma when compared with mild asthmatic and control groups (p < 0.05). Women with severe asthma were significantly more likely to have gestational diabetes and pre-eclampsia than were controls (p = 0.02 and 0.04, respectively). Compared with controls, patients with moderate and severe asthma were significantly more likely to be admitted for preterm labor (p = 0.02 and 0.002, respectively), to have their pregnancies complicated by premature rupture of membranes (p = 0.03 and 0.004, respectively), and to deliver by cesarean section (p = 0.005 and 0.0005, respectively). The occurrence of antepartum hemorrhage was significantly increased in severe asthmatics compared with controls (p = 0.04), however, the frequency of postpartum hemorrhage was comparable between groups. The neonates born to patients with moderate and severe asthma, were at significantly increased risk for intrauterine growth restriction (p = 0.03 and 0.02, respectively) and low birth weight (p = 0.02 and 0.01, respectively) compared to those of the control group. Also, preterm birth, low 5-minutes Apgar score and perinatal death were significantly more frequent in neonates born to severe asthmatics than in those born to the control group (p = 0.03, 0.04 and 0.004, respectively). There were statistically insignificant differences in the occurrence of congenital anomalies and respiratory distress syndrome in the neonates of the asthmatic and control groups (p > 0.05). From this study, it can be concluded that pregnant asthmatic women are at risk for adverse perinatal outcomes. The extent is variable and is related to the severity of the disease.