N-acetylneuraminic acid (sialic acid) storage disease is a rare autosomal recessive lysosomal disorder. Clinically two major forms exist, an infantile type with severe progression leading to early death, and a milder form (Salla disease) with a protracted course. Intermediate forms may also exist. Diagnosis rests on the determination of an excessive excretion of sialic acid in urine and concomitant storage in fibroblasts, the severe forms exhibiting the highest excretion and storage. We present clinical, morphological, and biochemical data on three non-Finnish patients with sialic acid storage disease. Patient 1 was a preterm infant with neonatal ascites, coarse face, hepatosplenomegaly, pale skin, and wispy hair. Vacuolated lymphocytes were abundant in a peripheral blood smear and he excreted large amounts of free sialic acid. High levels of free sialic acid were also found in cultured skin fibroblasts. He died at age 6 months from progressive respiratory insufficiency. Patient 2 was an 11-month-old Egyptian girl with coarse face, frequent upper respiratory tract infections, hepatosplenomegaly, and severe psycho-motor retardation. Sialic acid excretion was elevated, likewise the storage in fibroblasts. Histological investigations documented vacuolar storage in a skin biopsy and in iliac crest tissue. Patient 3 was a 16-year-old girl with slightly coarse face, severe generalized muscular hypotonia, ataxia, and kyphoscoliosis originally diagnosed as having post-partum asphyxia. She suffered progressive motor function loss and had dysarthria. Urinary sialic acid was elevated and a skin biopsy demonstrated vacuolization. The clinical variability of sialic acid storage disease is exemplified by these three cases. Simple urinary screening for free sialic acid facilitates the diagnosis. The degree of urinary excretion may indeed correlate with clinical presentation and progression.