Objective: To divulge a case of Williams-Beuren Syndrome (WBS). Clinical case: Toddler, male, 1-year old, referred to the Endrocrinology Unit of the Merida, Venezuela Los Andes University Hospital for presenting hypotonia and psychomotor retardation. At clinical examination he exhibited:weight: 8.3 kg (P10); height: 75 cm (P50); size genetic potential: 176±10 cm; normocephalic, with facial dysmorphia characterized by broad forehead, short and wide nasal bridge, slight palpebral and epicanthic obliquity, brown starry iris, long philtrum, small jaw, bulging lips and probable microdontism. Systolic ejection murmur in pulmonic root. Neurological examination evinced slight and harmonic truncal hypotonia and attention deficit. Ultrasound reported mild thyroid hypoplasia, thyroid profile being compatible with subclinical hypothy roidism. Hemodynamic monitoring confirmed multiple stenosis of pulmonary arteries and peripheral branches. Conclusion: Patient was diagnosed with WBS because of main branch and peripheral pulmonary artery stenosis concurrent with facial demeanor typical of this disorder. Its occurrence, likely sporadic and due to 7q11.23 deletion, attends one in 7500 live births. Subclinical hypothyroidism, associated to thyroid hypoplasia, is one of the most frequent endocrinological alterations found in these patients.