The purpose of this study was to assess the effects of spontaneous and instrumented deliveries, the baby's birthweight, the presence of stress incontinence and the woman's age and weight on bladder neck (BN) position and mobility using perineosonography, a simple non-invasive method, and to compare these results with those from continent nulliparous controls. Two hundred and fourteen women, including 74 nullipara, 29 para-1, 64 para-2 and 3, 16 with previous forceps deliveries and 32 with stress incontinence, underwent perineosonography with measurements of BN position and backwards/downwards displacement of BN using a two-axis calculation system. Results showed that bladder neck position undergoes a significantly backwards and downwards displacement on assuming an upright position. When compared with nulliparous controls, the bladder neck position at rest was the same in all groups of parous women in the supine/standing positions, but lower in patients having undergone forceps delivery (standing position) and in stress incontinent patients (both supine and standing); the bladder neck position during Valsalva was significantly lower in all groups of patients in the standing position, but the only significant difference in the supine position was seen in stress incontinent patients; the extent of bladder neck displacement was not significantly different between the groups, except in stress incontinent patients. A strong correlation (r = 0.66) was found between the relative importance of backwards and downwards displacement, but no correlation was found between bladder neck displacement and baby's birth-weight or patient's weight. It was concluded that compared to nulliparous continent patients, normal and instrumented delivery induces no modifications of BN position at rest, but is responsible for a lower bladder neck position during Valsalva in the standing position only. The extent of BN displacement is virtually the same in all groups of patients in both positions, except for stress incontinent patients, who have a significantly lower and more mobile bladder neck, the values of which overlap to a great extent (sensitivity of 78%/75% for a displacement > 14 mm) within those seen in continent nulliparous women. The correlation between the importance of backwards and downwards displacement is strong, making superfluous a two-dimensional coordinate system for routine BN position/mobility assessment.