Objective The purpose of this study was to analyze the profile of disorders presenting with neonatal hypotonia (NH) in an outpatient unit for genetic and metabolic diseases.

Methods Retrospective study of patients presenting with NH, followed in an outpatient unit of genetic and metabolic diseases. Cases were ascertained by a systematic search of clinical databases, over a period of 5 years (2003–2008).

Results We analyzed 31 patients, 61.3% female, medium age of 7.2 years old (yo) (maximum 17 and minimum 2 yo).

The most frequent cause of NH was Down syndrome (S.) (8 cases, 25.8%), followed by Beckwith-Wiedemann S. (5 cases, 16.1%), respiratory chain disorders (4 cases, 12.9%), Angelman S., Prader-Willi S. and Steinert S. (3 cases each, 9.7%), and finally orofaciodigital S. type 1, primary hypomagnesemia, Werding-Hoffman S., Smith-Lemli-Opitz S. and euchromatin duplication of chromosome 11 (1 case each, 3.2%).

The association of hypothyroidism with Down S. was present in 75% of the cases.

The etiologic diagnostic average age was 2.1 yo (maximum 10 yo, minimum 1 day, median 0.25 years).

In a follow-up of 5 years, only one 5th month of life patient (Werding-Hoffman S.) died as a consequence of pneumonia.

Conclusion More than 50% of the total cases of NH were due to Down S., Beckwith-Wiedemann S. and respiratory chain disorders. NH was more common in female patients. The majority of the cases were diagnosed before the 4th month of life and the mortality was low during these 5 years of follow up.