BACKGROUND: The 15-item Geriatric Depression Scale (GDS-15) is recommended for screening older people, but there are no large epidemiological studies using this instrument in the UK. We describe the age and sex distribution of GDS-15 scores in the largest ever UK sample of people aged 75 and over. METHOD: We used cross-sectional data from the MRC Trial of the Assessment and Management of Older People in the Community. The GDS-15 was offered to a representative sample of UK people aged 75 and over. Proportions of people attaining thresholds on the GDS-15 were calculated by age group and sex. Crude Odds ratios (ORs) for the effect of age and sex were calculated and the sex/age adjusted ORs estimated using logistic regression for surveys, at three GDS-15 thresholds. RESULTS: Of 21 241 (71.2%; 95% Confidence intervals (CI): 67.9-74.3) eligible people, 15 126 received the assessment including the GDS-15. Of these, 14 545 (96.2%; 94.7-97.2) completed > or =13 GDS-15 answers and were included in the study. Scores showed a marked right skew, with a median of 2 (interquartile range: 1-3; range: 0-14). 34.6% (95% CI: 32.1-37.3) people scored > or =3, 8.0% (6.9-9.2) scored > or =6 and 3.1% (2.5-3.7) scored > or =8. Women were significantly more likely to score above all three thresholds than men, as were older participants. CONCLUSIONS: Depression may be common in later life. The data provide a national picture of the numbers of older people who will score positively for depression in health screens which include the GDS-15, as recommended by the Royal College of General Practitioners.