This study aimed to observe the effects of ultrasound waves at different frequencies on abdominal fat tissue. External ultrasound-assisted lipectomy (XUAL) via both histologic and immunohistochemic examinations was used to assess adipose tissue alterations, including cells and collagenic fibers. The results, at the immunofluorescence level, show that ultrasound used at 1 MHz with a potency of 3 W resulted in no alterations or only limited cell destruction with collagen fibers intact. In contrast, when the ultrasound was 2 and especially 3 MHz, adipocyte alterations usually were evident. Massive adipose tissue destruction, confirmed using Oil red-O staining, was observed. In addition, at the immunofluorescence level, diffuse collagen fiber retraction was detected. This was particularly evident in comparisons with biopsies of intact control samples, which showed normal adipose tissue and intact collagen fibers. The results obtained using morphologic techniques, which do not allow fixation artifacts and include collagen observations, demonstrate that with the XUAL technique, ultrasound at 1 MHz does not induce cellular alterations. In contrast, both 2- and 3-MHz frequencies are capable of causing complete fat tissue disruption, including destruction of adipose cells and collagenic fibers.