||Professional responsibility in medicine exists since the beginning of medicine itself. The Hammurabi Code, which dates from 1728 bC, already mentions some articles related to the professional responsibility of the doctor. In all eras, laws and medicine haven been forced to adapt to all the scientific advances and social changes that haven been made. Medical responsibility has has had to change as well. The current approach of responsibility is not supposed to be anymore the search of "guilt" but the searching of all those factors that have influenced in a non desired attending procedure so that it has provoked in a patient the appearance of and adverse reaction, complications and sequels that could have been avoided. The aim of this thesis is to make quantitative and qualitative analysis of medical responsibility based on expert reports accomplished by the forensic doctors in the city of Barcelona from 2004 to 2009 which have been obtained from the archives of "Servei de Clínica Medicoforense de l'Institut de Medicina Legal de Catalunya". The mainlines have been basically obtained from the reports of the forensic doctors, however, there has been some cases where a computing followup has been made by getting the court sentences of the pursued procedures and, therefore, the court decisions. The statistics analysis has been undertaken as it follows: the descriptive statistics, which are mean, median, standard deviation, minimum and maximum have been used to study the quantitative variables. As for the qualitative variables, we have calculated absolute and relative frequency tables. In order to analyse relationship between two qualitative variables, it has been performed contingency tables between both variables, along with the corresponding bar graphs. To stablish if there was a statistically significant association, khi squared has been run, as well as likelihood ratios, depending on what was most appropriated at each situation. Whenever "age" as a quantitative variable has been involved in the analysis, Krskal-Wallis non-parametric test has been used, but only if the covariates had more than two categories, while Wilcoxon non-parametric test has been used in case it had only two categories. (eg Wasserman, 2006). Finally, a survival analysis has been performed, the aim of which was the analysis of how long it takes to happen a well defined event (eg Klein & Moeschberger, 2003) The most relevant results have been: The sampling consists of 283 expert/proficient reports belonging to years 2004-2009. In 89. 05% of cases, forensic's report is performed at a magistrate court's request. Talking about reasons of claims, it has been viewed that complaints about wrong therapeutical results are the most frequent ones (32. 86%), specially when patient remains with sequels. This is followed by bad surgery technique (19. 08%). Complications in clinical course rank third (13. 7%) and finally we find mistaken diagnosis. (11. 66%). The average age of affected patients by a medical malpractice is 48. 38 years. When referring to sex, 62. 7% are women while 37. 2% corresponds to men. There are more complaints related to surgical specialties than to medical ones, and among those, orthopaedic surgery and traumatology rank first, followed by gynaecology and obstetrics. Private medical centres own the 40. 28% of claims. The 28. 6% belongs to public health centres. The remain correspond to other kind of centres. 88. 34% Of claims are against doctors, while the rest of percentage are against other kind of professionals. Based upon the results we have obtained, we can confirm that the penal law is not the most appropriate law to ensue a likely medical malpractice claim. It is a process that generates stress, anxiety and insecurity to the doctor and to the family as well. Creation of arbitration tribunals and preventive legal medicine at hospitals could be part of the solution to that situation.