Hyperornithinemia, Hyperammonemia, Homocitrullinuria, or HHH syndrome (OMIM 23897) is an autosomal recessive inherited genetic disorder caused by mitochondrial ornithine transporter deficiency. Characteristically the syndrome display a wide clinical and biochemical variability where some differences have been observed in comparison with other urea cycle defects (UCD). Despite of this, treatment is based on the general recommendations for UCD and information regarding treatment and monitoring of HHH patients is limited. For these reasons, this work seeks to identify clinical, biochemical characteristics and response to established nutritional treatment in patients with HHH syndrome. For this, a literature review was carried out including 23 studies, among case reports and case series of HHH patients documented until 2019. The results show, a biochemical and symptomatic variability that does not seem to be conditioned by age, but that suggests that ornithine and homocitrulline are the main diagnostic biomarkers, as well as ammonium and homocitrulline could be the main follow-up biomarkers. The treatment showed wide variability in the modification in the amount of dietary protein and the dosage of the supplements, which, otherwise, suggest a positive response at the neurological and biochemical level, however, the lack of detailed information does not allow establish clear associations in terms of clinical, biochemical, or treatment in patients with HHH syndrome, so they should continue to be studied.