This study aimed to ascertain frequency rates and predictors of six problematic online behaviors (POBs) in an Australian sample. Participants (N = 1626) completed instruments measuring problematic online gaming, cyberchondria, problematic cybersex, problematic online shopping, problematic use of social networking sites, problematic online gambling, anxiety, depression and attention deficit/hyperactivity disorder (ADHD). Each POB was presumed to be present based on the cut-off score on the corresponding instrument and at least one indicator of interference with functioning. Generalized linear model analyses were used to determine socio-demographic and psychopathological predictors of each POB. The most common POB was problematic online shopping (12.2%), followed by problematic online gambling (11.4%), problematic use of social networking sites (6.0%), problematic cybersex (5.3%), problematic online gaming (5.2%) and cyberchondria (4.6%). Age group 27–36 had the highest rates of POBs. The intensity of ADHD symptoms predicted all POBs, whereas younger age predicted all POBs except for problematic cybersex and online gambling. Female gender predicted lower scores on the measures of problematic online gaming and cybersex. These findings have implications for age- and gender-adapted education, prevention and treatment efforts and suggest that specific POBs should be investigated separately instead of lumping them together under the umbrella terms such as “Internet addiction”.