Background <p>Tailgut cysts are rare congenital cystic lesions arising from remnants of the embryological postanal primitive gut. Familial clustering of tailgut cysts has been rarely reported, and the association with sacral dimple sign as an early diagnostic indicator remains underexplored. We report two cases of familial tailgut cysts in sisters who presented with sacral dimple sign.</p> Case presentation <p>Two female siblings of Asian ethnicity presented with sacrococcygeal lesions. Patient 1, a 17-year-old girl, experienced a 7-day history of localized tenderness and swelling over the sacrococcygeal region, with a palpable mass and a feeling of local fullness in the perianal area, accompanied by low-grade fever (up to 38&#xa0;°C). Physical examination revealed a posterior anal dimple ("sacral dimple sign") with marked tenderness over the presacral soft tissues, without bony tenderness. Digital rectal examination revealed a smooth, non-tender cystic mass palpable posteriorly, with intact rectal mucosa and no evidence of fistulous tract or induration. Magnetic resonance imaging (MRI) and endorectal ultrasound (EAUS) demonstrated a presacral cystic lesion with features suggestive of superimposed infection. Patient 2, an 8-year-old girl (the younger sister), was noted at birth to have a postanal dimple but remained asymptomatic. MRI and EAUS demonstrated disorganized soft-tissue signals posterior to the anal canal. Both patients underwent complete surgical excision of the cysts. Postoperative histopathology in both cases confirmed the diagnosis of tailgut cyst. Both patients recovered well postoperatively, and at 12‑month follow‑up, no recurrence or complications were observed.</p> Conclusions <p>Familial tailgut cysts, although extremely rare, may have developmental or genetic underpinnings. The "sacral dimple sign" should raise clinical suspicion for an underlying tailgut cyst. Early imaging evaluation and complete surgical excision can achieve excellent outcomes.</p>