The aim of our study was to describe the characteristics of patients with classical galactosemia in Croatia, with the description of patients with galactokinase deficiency and a patient who was a double heterozygote for mutations of the galactose-1-phosphate uridyl transferase (GALT), and galactose-4’-epimerase (GALE) genes. The study included 24 patients who were diagnosed with classic galactosemia from 1977 to 2020. Diagnosis was based on clinical presentation and galactose concentrations in blood and urine, and confirmed by measuring galactose-1-phosphate-uridyl-transferase activity and/or GALT gene analysis. Acute manifestations of the disease developed in 87% of patients in the newborn period, and one patient died. The median age at the onset of first symptoms was four days and for onset of therapy 11.5 days. At least one long-term complication occured in 78.3% of patients, including developmental disorders (68.2%), behavioral disorders (31.8%), speech disorders (55.6%), impaired intellectual abilities (46.2%), other neurological complications (40.9%), cataract (18.2%), and decreased bone mineral density (27.8%). Ovarian insufficiency occured in 66.7% of female patients older than 10 years. When comparing siblings, although a galactose-free diet was started earlier in the second-born children with classical galactosemia, the incidence of long-term outcomes did not appear to be related to birth order. In conclusion, this study shows that the vast majority of patients develop symptoms in the neonatal period, as well as long-term complications, despite strict adherence to a galactose-free diet. Many factors that affect the pathogenesis and clinical course of the disease are still unknown, which is why further research into classical galactosemia is needed.