To present clinical and laboratory findings in the case of a term newborn with conjugated hyperbilirubinaemia and to stress the importance of differential diagnosis.A term newborn delivered by caesarean section (birth weight 2550 g, birth length 47 cm, value of Apgar score 9/10) with good direct adaptation had on the first day of life increased levels of conjugated bilirubin (23 micromol/l), unconjugated bilirubin (55 micromol/l) and C-reactive protein 39.4 g/l. The diagnosis of mevalonic aciduria was confirmed by urine analysis (mevalonolactone 393 micromol/mmol crea, normal range <2.0 micromol/mmol crea; mevalonic acid 40.5 micromol/mmol crea, normal range <0.04 micromol/mmol crea).Mevalonic aciduria can be clinically distinguished based on symptoms of neurological involvement. It can also present itself with hepatosplenomegaly, lymphadenopathy, anaemia, leukocytosis, increased sedimentation rates and levels of C-reactive protein. In cases of conjugated hyperbilirubinaemia of unknown aetiology it is important to exclude mevalonic aciduria by urine investigation for organic acids.