Introduction: Fibromatosis colli is a congenital muscle tumor with an incidence of 0.4%. This lesion is fibrous involving the sternocleidomastoid muscle, discovered after a few weeks of life in a patient who had known or unknown perinatal trauma. Rarely bilateral, it evolves spontaneously favorably in a few weeks or months in the vast majority of cases. Objectives: The purpose of this work is to bring the interest in ultrasound in the management of fibromatosis colli. Material and Methods: This is a descriptive cross-sectional study covering a period of 21 months from December 2019 to December 2021 in the medical imaging department of the medical clinic "Marie Cuire" in Bamako. The variables analyzed were age, sex and ultrasound results. The ultrasound system used was General Electric (GE). Data analysis was performed using Excel software. Results: During the 21-month study period, 1260 infants were seen in our service, including 0.95% for cervical swelling. We had a male predominance with 8 cases out of 12 cases and the age of the patients was mainly between 21 days and 30 days. The diagnosis was made by ultrasound, which revealed within the Sterno-cleido-mastoid muscle (MSCM) a hypo-isoechoic or heterogeneous oblong mass or thickening without any other associated anomaly. Conclusion: Cervical ultrasound is a significant examination in the management of fibromatosis colli for diagnostic confirmation and therapeutic follow-up.