The prevalence and characteristics of research misconduct have mainly been studied in highly developed countries. In moderately or poorly developed countries such as Croatia, data on research misconduct are scarce. The primary aim of this study was to determine the rates at which scientists report committing or observing the most serious forms of research misconduct, such as falsification, fabrication, plagiarism, and violation of authorship rules in the Croatian scientific community. Additionally, we sought to determine the degree of development and the extent of implementation of the system for defining and regulating research misconduct in a typical scientific community in Croatia. An anonymous questionnaire was distributed among 1232 Croatian scientists at the University of Rijeka in 2012/2013 and 237 returned the survey. Based on the respondents who admitted having committed research misconduct, 9 admitted to plagiarism, 22 to data falsification, 9 to data fabrication, and 60 respondents admitted to violation of authorship rules. Based on the respondents who admitted having observed research misconduct of fellow scientists, 72 observed plagiarism, 69 observed data falsification, 46 observed data fabrication, and 132 respondents admitted having observed violation of authorship rules. The results of our study indicate that the efficacy of the system for managing research misconduct in Croatia is poor. At the University of Rijeka there is no document dedicated exclusively to research integrity, describing the values that should be fostered by a scientist and clarifying the forms of research misconduct and what constitutes a questionable research practice. Scientists do not trust ethical bodies and the system for defining and regulating research misconduct; therefore the observed cases of research misconduct are rarely reported. Finally, Croatian scientists are not formally educated about responsible conduct of research at any level of their formal education. All mentioned indicate possible reasons for higher rates of research misconduct among Croatian scientists in comparison with scientists in highly developed countries.