Because not all infants can be screened for DDH by experts, early diagnosis of developmental dysplasia of the hip (DDH) by primary health care professionals is important. We developed a broadband electroacoustic sound transmission-detection (sonospectrography) system and explored its utility in 22 patients (average age, 5.9 years; range, 0.3-14 years) with unilateral DDH in this preliminary study. Distinct from ultrasonography, the sonospectrography system functions by sound transmission and recording through tissues to differentiate between normal and abnormal hips. All hips were examined at four different hip and knee positions. The normal hip served as the control. The sonospectrography system was able to detect unilateral DDH. Dysplastic hips had lower sound transmission values when compared to normal hips in all patients and all four positions; however, the highest (X = 88.8 +/- 30.2 Hz) and lowest (X = 8.3 +/- 5.4 Hz) sound transmission mean values were obtained at different positions in the normal hips and those with DDH. Sound transmission values of dysplastic hips were always lower than that of normal hips when the hip and knee was flexed during measurements. Sound transmission values decreased with age. The sonospectrography system may offer a new noninvasive method in the diagnosis of unilateral DDH but requires further study of sensitivity and specificity of detecting dysplastic hips without subluxation in newborn infants.