A novel hybrid tomato plant, designated HMX5900 is disclosed. The invention relates to the seeds of tomato hybrid HMX5900, to the plants and plant parts of hybrid tomato HMX5900, and to methods for producing a tomato plant by crossing the hybrid tomato HMX5900 with itself or another tomato plant. The invention further relates to methods for producing a tomato plant containing in its genetic material one or more transgenes and to the transgenic plants produced by that method and to methods for producing other tomato plants derived from the hybrid tomato plant HMX5900.