Mucopolysaccharidosis-plus syndrome (MPS-PS) is a novel autosomal recessive disorder caused by a mutation in the VPS33A gene. This syndrome presents with typical symptoms of mucopolysaccharidosis, as well as congenital heart defects, renal, and hematopoietic system disorders. To date, twenty-four patients have been described. There is no specific therapy for MPS-PS; clinical management is therefore limited to symptoms management. The clinical course is rapidly progressive, and most patients die before 1–2 years of age. We describe a currently 6-year-old male patient with MPS-PS presenting with multiorgan involvement. Symptoms started at four months of age when he progressively suffered from numerous acute and potentially life-threatening events. When he was two years old, he developed secondary hemophagocytic lymphohistiocytosis (HLH), which was successfully treated with steroids. To date, this child represents the oldest patient affected by MPS-PS described in the literature and the first one presenting with a life-threatening secondary HLH. The prolonged steroid treatment allowed a stabilization of his general and hematological conditions and probably determined an improvement of his psychomotor milestones and new neurological acquisitions with an improvement of quality of life. HLH should be suspected and adequately treated in MPS-PS patients presenting with suggestive symptoms of the disease. The usefulness of a prolonged steroid treatment to improve the clinical course of children with MPS-PS deserves further investigation.