BACKGROUND: Multiauthorship and unjustified authorship have been documented in journals with wide international circulation but this has not been thoroughly studied in journals from developing countries. Revista Médica de Chile is published in Spanish and it contains about 40% of the clinical and biomedical manuscripts generated by Chilean authors. OBJECTIVES: To evaluate temporal trends in the number of authors per article in Rev Med Chile and authors' compliance with the International Committee of Medical Journal Editors (ICMJE) criteria of authorship (updated 2001). DESIGN: A retrospective analysis of the number of authors per article between 1969 and 2000; and a prospective survey applying a contribution checklist to authors of manuscripts published in the year 2000. "Justified authorship" was assigned to whom self-declared contributions to: 1) conception and design of the study, or acquisition of data, or analysis and interpretation of data; 2) drafting the article, or critically reviewed it; and 3) approved the final version. "Partial authorship" to whom lacked one of those 3 criteria. "Unjustified authorship" was assigned to whom participated only in data collection, or in diagnostic/therapeutic procedures, or in the statistical analysis, or in combinations lacking the main descriptors required for justified authorship. RESULTS: The number of authors in research articles increased in the last decade: From 3.9 +/- 1.6 (mean +/- SD) in 1969 and 4.9 +/- 2.0 in 1989 to 5.7 +/- 2.5* in 1994, 5.2 +/- 2.6* in 1999 and 5.4 +/- 2.2* in 2000 (*p < 0.05 compared to previous years). In contrast, it remained stable in case reports (4.1 +/- 1.9) and in reviews, public health or medical education articles (3.3 +/- 1.8). Among 921 authors surveyed (90% of authors in the year 2000), 51.2% qualified for "justified authorship", 42.3% for "partial authorship" and only 6.4% for "unjustified authorship". CONCLUSIONS: In a medical journal from a developing country, multiauthorship has increased mildly in research articles. Most participants complied fully or partially with the ICMJE criteria of authorship. Creditable authorship can be improved by continuous education and a critical attitude by the authors, readers, reviewers and editors.