Background Non-involuting congenital hemangiomas (NICH) are fully formed vascular tumors at birth, with a distinctive clinical, radiologic, and histopathological profile, and classically lack expansion or involution over time. We describe a series of NICH cases with atypical postnatal growth. Methods The authors retrospectively analyzed all NICH cases diagnosed from 2007 to 2017. We reviewed charts and photographic databases from our Vascular Anomalies Clinic. We included in the study all NICH with an atypical postnatal growth. Clinical data, imaging, and histopathology were analyzed. Results Eighty cases of NICH were identified. Nine presented with atypical postnatal growth after a stable period, at ages from 2 to 10 years (mean: 5.3 years). Two patients had associated pain; 5 patients showed new red papules on the surface of the lesion; 2 reported bleeding from the papules; and 1 developed a pyogenic granuloma. All patients had Doppler ultrasound and/or MRI compatible with NICH, and a confirmatory biopsy was performed in 4 cases. In treatment, 2 patients received endovascular embolization, and one required further surgery. Conclusions Non-involuting congenital hemangiomas (NICH) may develop significant postnatal growth over time (10% in our series), requiring closer follow-up for longer periods. The development of red papules, pyogenic granulomas, and superficial bleeding may be observed. Since this is a small series, we were not able to establish risk factors for NICH with postnatal growth.