Primary symptoms of Crohn’s disease usually include, among others, abdominal pain and cramping, recurrent diarrhea, fever and weight loss. The aim of this study was to show the effectiveness of ultrasound in the diagnosis and assessment of the extent of perianal complications in Crohn’s disease. Five patients (four boys and one girl) aged from 13 to 16 years, with prolonged pain in the perianal area, which worsened when sitting, were admitted to the Department of Pediatric Gastroenterology between 2017 and 2019. Each patient underwent intestinal ultrasound with a high frequency 7–12 MHz linear probe and transperineal ultrasound to assess the anal canal and the surrounding soft tissues. In each case, the echogenicity of the bowel wall was assessed for mural stratification and possible thickening. Anorectal fistulas were detected in all the five patients. Three patients (12 y.o. male, 12 y.o. female and 16 y.o. male) presented with perianal abscesses drained by fistulas. In the first patient the fistula was limited to the perianal soft tissue (22 × 23 mm); in the second patient it was localized within the ischioanal region (40 × 50 mm); and in the third patient (5–6 mm abscess) the fistula was with a hypoechoic fistulous tract reaching the sphincter. All of the patients were eventually diagnosed with Crohn’s disease as a result of further clinical workup. Ultrasound examination is a non-invasive, well-tolerated modality for the evaluation of Crohn’s disease activity and its possible complications, e.g. fistulas and abscesses. Ultrasound is especially useful in patients who require repeated follow-up investigations.