The paper presents clinical manifestations and results of cytogenetic examination of two patients with trisomy 8 mosaicism syndrome. The findings confirm the extreme phenotype variability of this syndrome. Both the first patient, a mentally retarded child with multiple dysmorphic changes, and the second, a 31-year-old woman with normal IQ and hypogammaglobulinemia as a predominant sign, revealed osteoarticular anomalies. Dermatoglyphic studies in both patients were typical for trisomy 8, and correlated with deep skin furrows. The chromosomal analysis was based on two types of lymphocyte cultures: 3-day and 2-day. A decreased percentage of trisomic cells in 3-day cultures in comparison to 2-day cultures may suggest the influence of environmental factors on spontaneous elimination of trisomic cells in vitro.