Vlasic started the season well with a bronze medal performance at the 2004 IAAF World Indoor Championships in March. She regularly reached the podium at meetings in the outdoor season and won the 2004 national championships. A Croatian record breaking jump of 2.03 m in Ljubljana put her in good stead for the 2004 Athens Olympics. However, when she competed at the Olympic high jump final she only managed eleventh place with a jump of 1.89 m. Following this, Vlašić did not compete for almost a year: she admitted that she was feeling lethargic and shortly afterwards she was diagnosed with a hyperthyroid condition.