We report on a patient with transient nonketotic hyperglycinemia (NKH). Onset, clinical features, biochemical and electroencephalographic findings were consistent with neonatal nonketotic hyperglycinemia. The normalization of clinical, biochemical and electroencephalographic features on day 9 without specific therapy suggested a transient form. At the last follow-up the girl was 13 years old, had a normal mental development, no EEG abnormalities or neurological deficits.